They can be out of their parents home yet still have some structure. 

Did he change any beneficiaries on retirement accounts (if he had any)If no paperwork was done, depending on how probate works in your state, you may not have any claim to an interest in the property unless he indicated that in a will. ie, in some states, if a parent is deceased, half goes to the spouse and half to the children.

my only concern is back in 2016 i converted the master bed room and bathroom in to a studio (not permitted) with its own entrance and kitchen i sealed off the entrance  to the main house and currently my parents live there paying me $500.00 a month i am worried that the studio will one hurt my appraisal (cant find any comps) so not sure what it will appraise at in its current state and second will the lenders have any issue's refinancing the home with the illegal studio ???

One of them is in college and her parent is on the original lease as a cosigner. 

Each of your parent can give you and your spouse (if married) 15k each without incurring gift tax i.e You and your spouse together can receive total of 60k (4 checks of 15k).If you are not married, you can get 30k. 

Every time my property manager knocks on the door no one answers or they have there kids do it and say there parents aren’t home.

I'd think a clean well taken care of place to live for $500-700 or whatever your rent range would be...would be no problem to find a good tenant - We lived the life of renters for a year and a half or so for the first time in our lives and quality rentals that are reasonable in Topeka is akin to winning a lottery ticket -- if you can't tell I was quite discouraged and very disappointed most of what's available if it was nice went immediately for ridiculous prices and most of the rentals were garbage for what was charged.My perspective comes as a home owner the instant I moved out of my parents house at 24 and then starting to own rentals at 26 and having never rented - so I'm probably again suffering from bias and a jaded perspective having been forced to rent. 

Have parents co-sign.

I know if you buy a house for your parents you can still take out a conventional loan but am not sure about buying a house for a sibling to live in. 

I don't feel like I own this tenant anything, as they have been bad neighbors above all else, but I am troubled by the idea of putting a single parent (who is out of work) in this situation.