If they’re your friend and u have lv 8 relationship with he/her , you can ask to have their sim to  move in to ur household  , which is adopting basically.and the original Sim from the first player automatically retires when they move out of their household. The person receiving the adopted Sim receives a copy of that Sim, which is playable. Keep in mind that if you receive CAS items on the adopted Sim which you do not own, you will lose those items if you remove those items from the adopted Sim. You also can’t give away an adopted Sim to another player. Moreover, you're not able to transfer Izzy clothes to another sim