Why wouldn't they just use most of the cast they have as voices as the live-action characters? Get a baby, a dog and Seth McFarland in a fat suit and you have Stewie, Brian and Peter. Seth Green fat and de-aged and you have Chris. Mila Kunis ugly'd up and you have Meg. Alex Borstein as Lois. Not hard.
It won't happen, it's not worth it if you ask me.