In my experience, the Eastern operated flights can go from D6 and the Fokker Farm, but are certainly more likely to park up at the far end of the D pier.

For reliability, EXT is 1x daily, BRS is 4x daily. So plenty more options from BRS when things go wrong. I would say it is probable that the risk of cancellation is slightly higher on Eastern compared to cityhopper, but don't think it's really enough of a difference to be a problem. I have flown dozens of times BRS<->AMS since the start of this wetlease and didn't have a cancellation yet.