I have a 4 year old lab/hound mutt from the pound.  He's a 75lb block of muscle that wouldn't hurt a flea.  This spring we got a female black lab puppy.  She loves to play with the older one but also likes to try and chew on his ears.  That doesn't go so well and eventually he goes into attack mode puts her in her place.  I suspect your dogs will sort it out eventually but it might be a bit painful for you to watch.  In my experience its best to stay out of the way.