Is it permissible to work in collecting rents for apartments inhabited by single individuals, some of which involve mixing between sexes in one apartment, where they share the kitchen and bathroom, and most of the residents are non-Muslims?

It is not permissible to rent out a house to a group of men and women, whether Muslims or non-Muslims, because it constitutes aiding in sin. It is also not permissible to work to collect these rents. However, there is no harm in renting out a house to non-Muslims for them to live in without impermissible mixing, because the landlord is not responsible for the tenant's unlawful actions for which the house was not rented.