All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
We did not clearly understand what you mean by his brother selling apartments with credit with Riba (interest and/or usury). If you mean that he will sell him the apartment by installments at a higher price than the price of purchase, then this is permissible provided that the sale is done with a definite and known price that does not increase. However, if you mean that he will give him a loan with Riba so that he would buy the apartment, then this is not permissible. We have already clarified in Fataawa 86701 and 82102 that it is forbidden for a Muslim to deal with Riba in order to buy a house or anything else except for a necessity.
In this case, you should advise your husband about this matter in a soft and gentle manner, then if he takes heed, all praise be to Allaah, otherwise, you would have done your duty and you will not be sinful.
Moreover, it is permissible for you to live with him in this house because it had become his property, because he is sinful for the loan with Riba but not for living in the house which he bought.
Allaah Knows best.