Re: Another newborn question...
Honestly I would just ignore their complaints. What are they going to do, call the police or a tow truck? You'd be long-gone by the time the police or tow truck actually arrived. Just fend off their complaints with polite refusals to move (eg "We'll be out of your way as soon as we can!") and don't drive off until you're satisfied with how the baby is in the seat.