Is it better for her to get married or to dedicate her life to her elderly parents?
Question

Which is better for 21-year-old muslimah, get married or didecate her life for her parents who are old already, and her two-brothers who are still young and need her financial support for their education?.
Praise be to Allah.There is no doubt that honouring one’s parents is one of the greatest ways of doing good and one of the widest gates of Paradise.
‘Abdullah ibn Mas‘ood (may Allah be pleased with him) said: I asked the Messenger of Allah (blessings and peace of Allah be upon him): O Messenger of Allah, which deed is best? He said: “Prayer offered on time.” I said: Then what? He said: “Honouring one’s parents.” I said: Then what? He said: “Jihad for the sake of Allah.”
Narrated by al-Bukhaari, 2782; Muslim, 85.
Just as honouring one’s parents is one of the widest gates of Paradise and earns the pleasure of Allah, may He be exalted, there is no doubt that keeping oneself chaste is also one of the most important matters that a person should be concerned with, especially at a young age when temptations are numerous and the individual fears for himself.
What appears to be the case, and is indicated by a great deal of experience, is that there is no conflict between the two matters that are mentioned here in the question. Indeed it is entirely possible to combine the two.
Taking care of parents with regard to matters where they need help, honouring them and upholding ties with them does not require you to dedicate your entire life to that purpose or that to let the opportunity of marriage pass you by when you are young. All you have to do is look at the nature of what your parents need from you. If they need you to serve them and they cannot do things for themselves and your younger brothers cannot do that, all that is required of you is to choose a husband who will let you do that. So instead of accepting a husband who will take you away from your city, choose a husband from the same city where you live. The closer his house is to your parents, the better it will be, so that it will be easy for you to go to them whenever they need that and take care of their affairs. Choose a husband who is kind and easy-going and will help you in that and not prevent you from doing it. At the same time you can organise their affairs in such a way that in many cases it will not be necessary for you to visit them every day, even if they are old.
Whatever the case, these are details that – it seems to us – can be arranged easily, in sha Allah.
If they need financial help for themselves or for your brothers, this is only as much as you are able to do. If you are working, you can give your family some of your salary or wages and you can stipulate to your husband that he should not prevent you from working or prevent you from helping your family.
If it so happens that after marriage you are less able to help them, then perhaps Allah will open another door to provision and goodness for them that will make up for that.
If they are not able to educate your younger brothers, even with help from people other than you, then what appears to be the case is that it is better for you to get married and keep yourself chaste, and to give that precedence over helping your brothers with their education.
Remember that Allah, may He be exalted, will help a person so long as he is helping his brother, so how about if you are keen to help your parents and your brothers. We believe that Allah is not going to deprive you of His help and guidance, and we think that He will grant you a way out from every worry and hardship. Allah says (interpretation of the meaning):
“And whosoever fears Allah and keeps his duty to Him, He will make a way for him to get out (from every difficulty).
3. And He will provide him from (sources) he never could imagine. And whosoever puts his trust in Allah, then He will suffice him. Verily, Allah will accomplish his purpose. Indeed Allah has set a measure for all things”
[al-Talaaq 65:2-3].
And Allah knows best.