Characters that cant do missions.

I'd suspect that those characters aren't in the 'Springfielders' category.

When anything is added to the game, its grouping parameters must be defined. So chars can be parts of families, or just stereotyped groups (like "B-list celebrities " )

Occasionally the parameters of those those labels are forgotten, or just done wrong so we cant see them as intended. But it's not YOU. There"s a lot of old skool bugs in this game. Try to be patient and wait for the occasional patch, as they usually come down the pipe.