You do not have to live in the same house with your parents-in-law. You can live in another house and that is not inconvenient from the Islamic point of view. However, your husband has to look after his mother and father if they are needy. Catering to his parents is his duty. The Glorified Allah commands:
“Your Lord decrees not to worship any but Him and to be good to your parents; if both or any one of them attain old age with you, do not say to them even ‘Uff’ neither neglect them, but speak to them with respect and be humble and tender to them and say: ‘My Lord, show mercy to them as they nurtured me when I was small.” (Al-Isra’ 17/23-24)
A bride does not have to look after her parents-in-law. There is no such order in the Quran or in Hadiths that says so. But one of the duties of woman is to treat her husband well. A woman that is not treating her parents-in-law well is also a woman not treating her husband well. Besides, treating the old ones well is one of the nice behaviors that our Religion advises.
The Prophet of Allah (p.b.u.h.) commands:
“He, who does not show mercy (and tenderness) to the young and respect to the elder, is not one of us.” (Tirmidhi, Birr, 15; Abu Dawud, Adab, 58; Musnad, 1/257)
“He, who shows mercy, sees mercy from Allah. (So) Show mercy to those on the ground and you will see mercy from the heavens.” (Abu Dawud, Adab, 58)
The brides should also put themselves in their husbands’ shoes. How would they like to be treated, they should treat their parents-in-law in that way.
Come together with your fiancee/husband and plan how you can treat them in the best way. You definitely do not have to live in the same house; but if they are needy we advise you to hire a house close to theirs. If you behave them well for the sake of Allah, Allah will bestow a happy family and marriage in this world upon you, as well as Gardens (Heaven) in the hereafter, inshallah.
For further information, please refer to: http://www.islamandquran.org/research/subsistence-money-of-women.html