Is Assisting in Sin a Sin?
Question

I have a health social worker who helps with the family's health and other needs.
He at times asks us for parking in our driveway to watch an Australian rugby league game that's nearby as the street parking is occupied extensively at this time.
Note these games have men exposing their thighs, music, mixing, serving of alcohol and are known for having cheerleaders strut and dancing.
I'm thinking that it is cooperating in sin but then I play out in my head what I would say then feel too shy to tell him as he's helped us & have a professional relationship with him. I know I shouldn't. And I am adamant not to next time. How should I approach this in the wisest best way?
Also I know someone who is intending to study taking out a student type loan that can accumulate interest if not paid within a year or so. I haven't asked whether they'll make the payment on time or not. Although it is most likely that they'll delay it.
They are a family member & I've let them do the entry test for that qualification on my laptop. Have I facilitated in sin?
If someone is studying in this form through Riba should I bar them from using my laptop?
Should I apply the "leave doubtful matters and stick with certainty" rule here even if it may cause some conflict? Or am I overthinking it all?
Praise be to Allah.Is it forbidden to help others in sin? 
It is forbidden to help others in sin, because Allah, may He be Exalted, says (interpretation of the meaning):
“Help you one another in virtue, righteousness and piety; but do not help one another in sin and transgression. And fear Allah. Verily, Allah is Severe in punishment” [Al-Ma’idah 5:2]
Additionally, the Prophet (blessings and peace of Allah be upon him) said: “Whoever calls people to guidance will have a reward like that of those who follow him, without that detracting from their reward in the slightest, and whoever calls people to misguidance will have a burden of sin like that of those who follow him, without that detracting from their burden of sin in the slightest.” (Narrated by Muslim, 4831)
There are other texts which prove that the one who helps someone else in sin is also sinning , such as the text which curses the one who records Riba and the two who witness it, and the curse on the one who carries alcohol (to someone who will drink it) and on the one who presses (the grapes etc with which it is made), and so on.
Nonetheless, not every kind of help is prohibited; rather what is prohibited is deliberate help in which the one who offers it intends to help the person in his sin, or direct help such as carrying alcohol or writing down contracts involving Riba.
With regard to indirect help, when one does not deliberately intend to help in sin, this is not prohibited; if it were to be prohibited, it would cause a great deal of hardship to people.
For example, it is confirmed that it is permissible to interact with the disbelievers in terms of buying, selling, lending, borrowing, and holding items in pledge, as is indicated by the authentic Sunnah, even though this involves indirectly helping them (in sin), because it is benefitting the disbeliever in financial terms, and enabling him to use that wealth in prohibited things such as Riba and the like, yet despite that Islamic teaching overlooks this kind of helping.
Categories of helping in sin and transgression
Dr Walid Al-Minisi, a member of the Council of Islamic Jurists in America, said:
“The issue of guidelines on helping in sin and transgression was the subject of a lengthy discussion and debate among the members of the Council of Islamic Jurists in America, in its fifth session held in Bahrain in 1428 AH.
To sum up the conclusion they reached: helping in sin and transgression falls into four categories:

Direct and intentional help, such as someone who gives alcohol to another person with the intention of helping him to drink it.
Unintentional, such as selling prohibited things that have a permissible use, if there is no intention to help them in using them in prohibited ways.
Intentional but indirect, such as someone who gives another person money with which to buy alcohol. Indirect manslaughter is also included in this category .
Indirect and unintentional, such as someone who sells things that may be used for lawful or unlawful purposes, and does not intend to help those who use them for unlawful purposes, such as someone who gives another person money not for the purpose of buying alcohol. If he buys alcohol with it and drinks it, there is no sin on the one who gave him the money, so long as he did not intend to help him with something unlawful.

This fourth category also includes buying and selling and renting from polytheists and Muslims who are evildoers, and giving money to them in charity.
The decision of the council was that the first three types are prohibited and the fourth type is permissible, which is the one that is not direct and not intentional.”
An exception is made from the fourth category in cases where it is known or thought most likely that the person who is helped will use it for sinful purposes. For this reason many of the jurists prohibited the sale of grapes to someone who will press them for wine, and the sale of weapons during times of turmoil, even though grapes and weapons may be used for both lawful and unlawful purposes.
Therefore Shaykh Al-Islam Ibn Taymiyyah (may Allah have mercy on him) said: 
“Every garment that he thinks will most likely be used for sinful purposes, it is not permissible to sell it to or sew it for one who will use it for sinful and wrong purposes. … The same applies to everything that is basically permissible, when it is known that it will be used for sinful purposes.” (Sharh Al-‘Umdah, 4/386)
Going back to your question, it seems that offering direct help to this employee would mean someone taking him there in his car, or buying him a ticket of admittance, and the like.
As for simply allowing him to park his car, this is indirect help, and there is not necessarily any connection between that and the sin; he may not go to the match, or he may go but not commit any unlawful action, such as looking at ‘Awrahs or mixing (with women) in a prohibited way. In principle, it is essential to differentiate between going to commit sin and going to do something permissible that may be accompanied by something sinful, as the jurists differentiated between someone who rents out his house to be used for sinful purposes, such as making it into a tavern, and someone who rents out his house for permissible accommodation, but alcohol is drunk in it. The former kind of renting is prohibited but not the latter.
Undoubtedly, differentiating between direct and indirect help will vary from one issue to another. So the scholar should try to examine the case, with reference to what the jurists have mentioned about similar cases.
To sum up: letting this employee park his car in your driveway is not directly helping him in sinful actions such as looking at ‘Awrahs or listening to music, and other evils that are present in the stadium; rather it is helping him and comes under the same heading as helping him by selling food, drink and clothing to him. That is not prohibited on the grounds that it may help him to remain strong and healthy and enable him to commit unlawful actions, because that is indirect and unintentional help, therefore Islamic teaching overlooks it and permits us to buy and sell and engage in commercial transactions with the disbelievers, as mentioned above.
Assisting someone take an admission exam using your laptop for loan-financed studies
There is nothing wrong with allowing your relative to take the acceptance test for admission to his studies using your laptop, even if he is going to pay for his studies with an interest-based loan . That is because studying is permissible, and you are only helping him with that, not with the loan.
Rather it is forbidden for him to use your computer to get this unlawful loan , because that comes under the heading of helping him with that sin.
You should understand that whoever takes out an interest-based loan, despite the fact that it is sinful, takes possession of the money that he borrows and it is permissible for him to make use of it with regard to his food, drink, accommodation, studies and other things, and he does not have to get rid of any of these things. So there is nothing wrong with you helping this relative and others with regard to permissible studies.
Can you stipulate late payment fees in case of interest-free loans?
Interest-free loans are prohibited if it is stipulated that a penalty be paid in the event of late repayment , because this comes under the heading of approving of Riba, along with the possibility of actually falling into Riba.
It says in a statement of the Islamic Fiqh Council belonging to the Muslim World League in Makkah, issued during its eleventh session, statement no 8:
“If the lender stipulates that the borrower has to pay a sum of money as a financial penalty of a fixed amount or a specific percentage, if there is any delay in repayment beyond the time agreed upon by both, then this is an invalid condition, and he is not required to fulfil it; indeed it is not permissible, regardless of whether the one who stipulated it was the bank or anyone else, because this in and of itself is the Riba of the pre-Islamic era that the Quran forbids.” 
And Allah knows best.