Is the real estate broker's commission unlawful if the tenants commit unlawful acts on the leased property, and is the broker sinful for facilitating that?

The basic principle is that it is permissible to act as a mediator between the owner and the tenant, as long as it is not rented to someone who will use it for forbidden acts, such as making it a place for prostitution or drinking alcohol, and so on. This applies whether this condition is stipulated in the contract or known through an indication. Therefore, if the tenant does not stipulate the use of this house for disobedience, or if their condition does not indicate that, then there is no objection to renting it, and there is no objection to you being a mediator between the owner and the tenant and taking money for that.