Does A fight back? Or just take it because she is a girl? I am guesing E is not quite big enough to hold her own yet.

Only asking because, as bad as it sounds, I think that it was when DS2 got big enough to fight back and I just left them to it a bit more, that it got better. I tried being super attentive with DS1 too, but I am pretty sure in the end they had to sort it out for themselves. That probably isn't very helpful when there will be another child who will need to find their place soon, but you may just need to play referee for a while longer. Hopefully as they are so close in age it won't be long before they all become friends again.