Nice idea, but make sure that it dosen't make them do something random every time you switch. If yo haven't played as them in a while, then have them doing something. If you recently played as them, switch to them where they were where you left off. Also have them maybe walked/drove/rode a lil distance based on time passed. Also, if the character is in sight make sure you can switch to them without their location being moved. And if you do not plan on letting you find other characters around as who you play as, make sure they don't spawn where the player is near.
If you do make them findable when not playing as them (Which is best) then just make them spawn at the hospital if you switch to them.
Just some suggestions so the mod can be it's best, good luck.