Your 1 year old should still be rear facing. Until he’s 2 *at least* but I would rear face longer than that honestly. My 2.5 year old is still rear facing. I have diono radians. They’re expensive af but that’s the only car seat I can fit 3 across

I have a Ford Focus and I’ve had 3 car seats in the back of mine. I’m sure an impala would fit 3 just fine.

I have a 2013 Ford Focus st it’s a sports car and it’s very compact and small on the inside I can safely fit two car seats one rear one forward and a booster. I know it’s not an impala but my cars small so you should have no problem