Yes they do! And I think once they retire you can play them! (Don't hold my word for it but I'm almost 100% sure you can:) have fun playing!

I am on level 16 and have 6 sims in my house. 2 of them are married and they have 3 children. One of the children now is an adult but I can't control him. And the last one is a sim that I add because I purchased The add sim thing.

Yes

Same here, it gave me a new sim instead, that sucks

so if you purchased the add sim, you will create new sim instead of choosing one of your children?

Yes