If the mold were from your enclosures, it would show up near them first before spreading from that as the center of it. With it only being far away from them and not surrounding the cages, I would assume it is either preexisting mold issues or related to faulty/dripping plumbing in the walls causing a new mold issue they want to avoid dealing with.

No legal experience here, but if you pay a pet rent fee and/or they knew about and agreed (especially written) to you having them before/when they arrived, it seems like they shouldn't have much ability to do what they're trying to do. It seems like either of those cases would mean they knew the risks of allowing it and agreed to them. Pet rent is part of your contract and there's usually terms to protect tenants from sudden rent changes or terms changes, so that might be relevant and something to review the wording of.

Talking to a lawyer would probably be your best move. They'll know for sure, especially for your area, if it is legal or not and what recourse you have.

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