I'd like to at least see Franklin included in one of the movies. He's been a presence in the Fantastic Four comics longer than many of us have been alive, writers rarely treat him like a burden to the team, and he's one of my favorite supporting characters. He kinda deserves it, even if we have to wait until the second or third movie to get him.
Valeria, though? I like her, but let's not walk before we can run. You gotta introduce the big brother before you can bring in the little sister. Plus having a super genius 3 year old presents a laundry list of issues a live action film would have to address that I don't feel like getting into in this post.