Some people post the same topic in both the renters forum and the landlord forum simultaneously.

Both are very common and its not unusual for both to happen simultaneously. 

My advise is to immediately start getting the place ready to re-rent and advertise, and simultaneously get a lawyer (or yourself) to send an official letter outlining everyone's responsibilities and remedies.

Most markets won't experience real estate value declines and rental declines simultaneously unless the population base is contracting, i.e. the death of a boom town, or a demographic migration (say from the Rust Belt to the Southwest).

So, you need to cover your butt.You could simultaneously serve them the 3 day notice to cure or quit, and the 60 day notice of termination and double cover your rear.But, I don't think you can trust these people, and now that you're aware that they can't be trusted, you could end up liable - because you knew about it. - and you know they lie and will probably continue to house too many people to be safe.

I totally agree with you that there is no point in giving someone a tax free gift every year, however I think my family member finds the prospect of multiple simultaneous vacancies a little overwhelming.

So, whoever inherits this guy just has to give him 30 days notice to vacate, and simultaneously give him notice to evict for nonpayment of rent.  

Simultaneously, no one is going to declare income and pay taxes on it, if it isn't real, but all sorts of people might make up all sorts of boastful income claims ...if they don't have to pay taxes on it.

The key is to have written rental criteria that complies with non-discrimination laws and fair housing laws, to measure all applicants against the same criteria, and to follow the requirements of landlord-tenant law for your jurisdiction.My wife (a licensed realtor) always tell me we are not allowed to process multiple applications simultaneously.

Better to get the tenant out and get your unit rented while simultaneously trying to collect the back rent.If you've already accepted then you may need to start the process over again.