First, J Bell won't be splitting carries with Blount. He plays for Detroit and he'll be splitting carries and catches with Bush. However this may be one of those rare backfields where both guys are startable, simply because of that prolific offense. It's also a dream matchup at home vs a team that can't get going.
Jennings has a much worse situation, because it's reasonable to conclude the Giants will get behind quickly in this one, and that means Eli slinging the ball. I don't think it's even close that you'd start Bell. Also, it appears that Bell may be the #1 in this platoon, not Bush.