Linda, I think it will work out just fine! Buddy and Beau are securing their place in the pack order.
Jack still has to remind Max who's boss now and then. When I hear a certain tone in the play-growl start to change- I intervene and play big-bad-boss
Right now I'm guessing that Buddy and Beau are sensing your protectiveness and attention to gambler and they may be a little jelous. This will pass as everyone settles in and Gambler secures his place in the household.
I'd do what you are doing and keep a good eye on them when they're all interacting.
Right now Gambler really is a baby and the older two may be feeling a little insecure with the big change in their world.
It's going to be natural for Buddy and Beau to excert themselves to keep their pack order in place.
It won't take them very long to figure out that Gambler can't dominate or threaten them.
Pay some special attention to Buddy and Beau and praise them lavishly when they are gentle with Gambler. Retain your position as leader and things will all fall into place. (which I am sure you are doing anyway)
I was pretty nervous and unsure of how Jack would react to Max. It was easier for Jack though because he was the only other dog. Buddy and Beau have each other and a well established relationship.
I am sure with your guidance and reassurance, Gambler will be hanging off their lips and being gently nose-rolled in no time
It's amazing how quickly they all establish and get comfortable with their roles, even though from time to time you'll see them putting each other in their places.
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Aaawwww Linda thats a real adorable pup you have... to cute,,, great pics to....
I've Been Frosted
I've been frosted! 
