Rob was still colostomized at the time, so it wouldn’t have been too difficult for the Grundys – or anyone else – to beat the crap out of him.
But you are right, it was strange that with her husband and his family present, it was two non relatives who came to Emma’s assistance, although I was pleased for Jazzer to be given something to do.
I’m guessing it’s to do with the character limitation (no more than 7 actors in one episode I think). But it could be explained logically as well. I have no idea about the layout of the bull but the Grundys were perhaps in the faraway corner of the pub and David and Jazzer were in the bar near the toilets. I for one thought it was delightful to get to her Jazzer throwing Rob out. “And don’t come back PAL”.
I presumed that the rest of the Grundy clan were in the Hassett Room or some other dark corner of the pub whilst Rob was hanging around one of the bars (pubs often used to have a saloon bar and a lounge bar and I’m sure that I recall Sid having to go through to the other bar to serve one of the Booths (Neville or Nathan). So it’s possible that the Bull has two bars and a restaurant.