What is the ruling on admitting a man or woman to the marital bedroom?
Question

                I wanted to check can a newly wedded couple or even normal husband and wife allow some one else to use their room or bed for sleeping purpose? ex: my Mother in law uses my bedroom in my absence for sleeping purpose. i came to know from sources that it creates differences between the husband and wife please help as this is back of my mind every day and i am facing a few minor issues with my husband because of my mother in law so its disturbing me even more.
Praise be to Allah.Firstly: 
One of the things 
    concerning which there can be no doubt is that the marital bedroom is 
    particularly private; it is the wife’s chamber and private space, the 
    innermost part of her house, where she takes off her clothes and is alone 
    with her husband, which is something that she cannot do anywhere except in 
    this place. 
What makes this place even 
    more private is that it is where she keeps her private clothes, cosmetics 
    and adornments, and things that have to do with intimacy between husband and 
    wife, which no one else should see, as they are regarded as being among the 
    most private aspects of the marital relationship. 
What we have mentioned is 
    the basic principle, and no one should go against it, but there may be 
    specific circumstances which dictate allowing a relative to enter this 
    private space, either because the house is small, or because they need to 
    use the room for one of the women to sleep in, because it is more private 
    than other parts of the house, or for some other reason, but that permission 
    is subject to certain conditions: 

    1.That there should be a real 
    need for that

    2.That the underwear of the 
    couple should not be visible, or anything else that may cause embarrassment 
    if it is seen

    3.That the person to whom 
    permission is given to enter should be trustworthy, lest he mess about with 
    private things in the room or tell others about it

    4.That the husband should give 
    permission for this person to enter. If he refuses then that should be 
    heeded and one should not go against that. Similarly, the husband should not 
    allow anyone to enter his wife’s bedroom if she dislikes that, unless it 
    cannot be avoided, and the one who enters should be trustworthy, such as his 
    mother or sister and so on, and he should ask his wife for permission and 
    put her mind at rest. 
Whatever the case, the 
    conditions that we have mentioned here are subject to ijtihaad, and the 
    purpose of them is to protect the privacy of the family members, with 
    particular attention to the marital relationship, and protect it from being 
    messed about with or from breaches of confidentiality and disclosure of 
    secrets. 
Muslim (1218) narrated that 
    Jaabir ibn ‘Abd-Allaah (may Allaah be pleased with him) said: The Messenger 
    of Allaah  (peace and blessings of Allaah be upon him) said: “Fear 
    Allaah with regard to women, for you have taken them as a trust from Allaah, 
    and intimacy with them has become permissible to you by the word of Allaah. 
    Your rights over them are that they should not allow anyone whom you dislike 
    to sit on your furniture. If they do that, then hit them, but in a manner 
    that does not cause injury or leave a mark.” 
Shaykh Muhammad ibn Saalih 
    al-‘Uthaymeen (may Allaah have mercy on him) said: The Prophet  (peace 
    and blessings of Allaah be upon him) explained their rights and duties, and 
    said: “Your rights over them are that they should not allow anyone whom you 
    dislike to sit on your furniture” meaning, they should not allow anyone to 
    enter upon them where they sleep or elsewhere, if you dislike people sitting 
    on the furniture in your house. It is as if – and Allaah knows best – he was 
    coining a similitude, meaning that they should not honour anyone whom you 
    dislike. This is going against you by honouring one whom you dislike, by 
    allowing him to sit on the furniture, or offering food to them, and so on. 
    End quote. 
Sharh Riyaadh 
    al-Saaliheen (3/126) 
Secondly: 
With regard to believing 
    that if someone sleeps in the marital bed that will cause problems between 
    the couple, this is a jaahili (ignorant) belief and a myth that the Muslim 
    should be above accepting because of his belief in Tawheed. There is nothing 
    in Islam that supports this idea, and there is nothing in real life that 
    confirms it. 
Thirdly: 
With regard to your 
    problems with your husband and his mother, this matter needs to be dealt 
    with wisely and properly by you. Seek to earn your husband’s pleasure by 
    being kind towards his mother, and seek to earn his mother’s love by dealing 
    with her kindly, giving her gifts, and speaking nicely to her, because a 
    kind word and good treatment win hearts. Seek reward from Allaah for putting 
    up with annoyance from your husband’s mother and seek to please your 
    husband; perhaps Allaah will create love and compassion between you and her. 
    Seek the help of Allaah to fulfil your husband’s rights and to be patient in 
    putting up with difficulties, and expect ease after hardship, and relief 
    after difficulty. 
For reasons why the 
    husband’s mother may not like the wife, and ways of dealing with the 
    problems that result from that, please see the answer to question no.
    84036. 
And Allaah knows best.