Should children over 18 living at home, sign a rental agreement

Mine won’t. The first went far away for college after graduation and has never lived with us since. The second is in military training right now, but she’ll live with us when she returns, and she won’t be paying rent while she juggles work, school, and deployments. If I had one who entered the work force but just couldn’t afford rents in the area (which are mind boggling), I would think they could pay their own bills like insurance and phone, etc, and would expect them to help around the house, do their own laundry and such, but I wouldn’t be charging rent let alone making it formal. If they were just squatting and stalling on adulthood, they would be invited to find other accommodations. Launching is harder now, but coddling too much doesn’t help anything either.