-They may or may not be consulted on character-development.
It's how I got control of Natasha Rez and Elias Santos in The Walking Dead: Northwards.
-But I'm Co-GM, I do that. I also have experiance doing that. (sorta)
After getting control of 3 or more players, I start using a more comical -less serious- narrative.
+None have broken the 4th wall, yet.
OTOH, I've never been comfortable RPing a shred of romance between any two characters I happen to play at the same time (although I do sometimes imply some backdoor-romance), unless ofc I crank-up the silliness.