We are arriving into Newhaven Port from Dieppe at 9PM, with a group of 9. (That is a Sunday). Ideally, we would like to rent a car. Do we have any options for transportation from this area?
A car for nine would be impossible to obtain. How much luggage? Even a van might be too small. I would think you might need three cars. With that size of group, have you consider a private car service?
There are trains to London and Brighton
http://www.nationalrail.co.uk/
and you can get buses to local towns
https://www.dfdsseaways.co.uk/customer-service/our-ports/newhaven-port
Dieppe to Newhaven seems an unusual choice without your own car and 9pm on a Sunday. Good luck with that.
Newhaven is a small town with few facilities and there aren’t any car hire offices there. The closest would be Brighton, 30/40 minutes drive away and few offices are going to be open at that time of night on a Sunday. You will need several cars for 9 plus luggage.
I wouldn’t recommend spending any time in Newhaven, as it’s a dump, not to put too fine a point on it. Take taxis to Brighton and hire cars early Monday morning.