You SHOULDN’T need a physics asset for that- See the blue boxes in the base level, I don’t think they have one. If you’re giving them collision and mass as far as I know that should be enough. Failing that, you could try giving them collision with pawn on top of that and try to push them with your character.
Also, it’s not too bad to just make a single physics asset if you wanted to do that and throw it on all of them.