Does anyone know of a reputable car service for a party of 6 to transport us from Nuremberg germany to Prague?
Look at CK Shuttle - you can configure a private transfer for that itinerary on their website.
Check also direct bus connections from Flixbus or train connections via Regensburg (group tariff): https://int.bahn.de/en
I've done that trip twice by train. It's been a while since I drove in the Czech Republic, but the roads weren't great.
Easy drive nowadays - A6 into Česko E50. E50 is a toll road. You can pay the toll online. Driving in Prague with traffic, street cars, one-way roads etc. can be a little hectic.