Introducing a new horse to herd

Question
I have a 17 yr old mustang horse and a 3 yr old donkey (owned both for 2 yrs) we just last week got a 20 yr old pony, we would like advice on how to introduce pony into herd? Pony is in their pasture but in barn stall, we have taken the pony out in evenings into a small paddock we put up for him so we can watch interaction through fence with each other. My horse being the boss in the field has sniffed and left for the most part, but today he made 2 (what i call bluff charges) at the paddock where pony is. The donkey stays at paddock smelling and trying to poke his head through fence. The pony doesn't react much at all to any of this...not even to my horse charging towards the fence (my horse did stop charge right at fence (bluff charge or showing dominance? ) Any advice on a safe way to put together and how to go about it. Thank you

Answer
feed the pony so he is not hungry, then put out 5 or 10 piles of hay (half flakes or so each) put these at least 20 to 30 feet apart so your two will have lots to think about, then let the pony in the pasture and you leave and stay out of it.  They will work it out.

Anytime you put a new horse in, there is always a chance of a kick, cut, bite or fence crash, but if you put the hay far apart and not close to any fence, the dominant one will chase pony off each pile and there will be enough piles so no one has to defend any food.

they should be fine, don't try and help or save, you will make it worse, just give the herd something to do (check out all the piles of food) and let the pony out that is not hungry and they should work it out.

Rick