Cosigners lease agreement for +65 year olds in NYS

[Adam LaPorta]

I have a tenant who sold me my house and is currently renting from me. 85 years old, great person, but in and out of the hospital last year and potentially this year too. Is not interested in leaving but is interested in leaving on their terms. I want a full year-long commitment to protect our investment. I was thinking of a cosigner lease from a family member...thoughts? Upstate NY area.