I have a duplex under contract which is being sold by an elderly woman who Is living in the larger of two units. She wants to stay where she is for undertermined of time after closing until her new living arrangement is set and has agreed to sign a lease at closing. Should I be requiring a security’s deposit from the seller and soon-to-be tenant as well?
Yes, but be careful with terms. "Undetermined" might be way longer than you want, and you should make sure the lease is yours and includes provisions for raising rent, eviction for cause, etc.