Basically, I had one of my Sims marry another Sim from a different player and requested that the player allow them to move in, which they did. But, Now to send that has moved in won’t on his last treat so he can’t retire.
Contacting EA will be of little help, they will tell you what they ALWAYS tell people, REINSTALL your game. This is the default lazy answer given to all issues with all EA games, which typically does NOT work. If they get enough complaints, they will eventually have a "fix" patch or update.
Your game is glitched, contact ea through https://help.ea.com/en/contact-us/?product=the-sims-mobile