The damage being caused to the property can be actionable as "waste" as it is destroying the value of the real property. This means that you can ask the court to order an injunction requiring that the brother in law act reasonably (you will need to identify what conduct is necessary to address).
Bringing a motion before the probate court to revisit this living situation based on changed facts and circumstances appears to be the most efficient mechanism to address these issues. What I can see are issues of:
trespass (noise affecting your tenants)
violations of the court order (if you can identify specific issues in the order that are being violated, either by the mother or brother in law)
I would still recommend hiring an attorney to draft and argue this motion to give you the maximum opportunity to succeed given the complexity of this issue, this would be a limited scope of representation
Given the facts as you have posted them, it seems you would have a reasonable chance of success, but local counsel can review your facts in detail and give you a better evaluation as this type of motion will be very fact specific.
Unfortunately, some APS departments are unfortunately slow to act, either based on policy
or resources, and will allow an elderly individual's assets to be drained prior to intervening. I am sorry to hear they are not willing to be of more assistance in your case.