Is it permissible for the wife to object to her husband's brothers being granted ownership of apartments they inhabit rent-free, and to be content with their residency therein without ownership, despite pressure from the husband's family to transfer ownership to them?

Your husband is not obligated to transfer ownership of the apartments his siblings live in to them, nor is he bound to obey his parents in this matter. However, if he wishes to please his parents and maintain ties with his siblings by gifting them the apartments, you have no right to prevent him as long as he continues to provide for you adequately. Your husband's eagerness to honor his parents and maintain kinship ties with his siblings is commendable and a righteous deed. Whatever he can do to show them kindness, without harming himself, it is preferable that he not withhold it from them.