hi
i probably shouldn't answer because i'm not the best one to answer this one.. but...what i can say is this.. if they are fighting, i think you would know it.. it's very easy to tell if they are fighting.. some of mine have gotten into it a few times [and i did stop it very quickly] so i can say there's no mistaking two chins fighting.
sorry but i don't know what grappling is... and as for jumping on each other's backs.. that i dont' know about either,,