I spent way too much time thinking about this. Parker, Porter and Preston are probably not the ones who are switched. The twins, as previously said, would be hard to do a switcharoo with them. Also those three look a lot alike.
It could be Penny.
Juanita and Celia look fairly similar, but you certainly are supposed to think that it's them (Flashing to them running right after the switcharoo is announced)
They showed Susan holding Julie, but I doubt that they'll do it with an adult child. At that point, you're already raised, and they'll likely do this with a child who is younger. This way there can be a custody battle.
Bree is probably safe, for the same reason I don't think its Julie.