A friend of mine have bought a flat in Renaissance Aviriti and he is happy with the investment as the quality of the building,amenities and Location seems good and hopes he ill get good returns back.

Write up a "Letter of Intent" (LOI).

This is a B+ unit in a B+ neighborhood and these tenants have been in place 2 years with relatively few problems and no intention of moving out.  

I changed out the filter a month ago, ill change it out again.

Interpretation of the law and it's original intent seems to be a lost art when it comes to an increasingly activist judiciary, so whatever the law seems to be today may be very different tomorrow.  

You should also understand that according to Oklahoma law, Wholesaling is illegal unless you have the means and intent to actually purchase the property even if you are unable to reassigned.

My main concern would be that if the landlord is to ill to cash the rent checks, what else is he neglecting.

(You will have to check your state laws).I recently had a tenant that would not sign a new lease, nor would she give any indication as to her intentions. 

Did your husband give proper notice to the company about his intent to leave their employment?

Post notice of your intent to enter under the time-frame prescribed by law, be it 24 or 48 hrs or howevermuch time.