they really are so much bigger and more rambunctious than he is... I let them
sniff each other, but no playtime together for a bit until the bigger kids can be
That's understandable. I bet it won't take them long though. My crew are pretty nosey & noisey when meaning newbies but within a couple hours to a couple days they always chill a bit. Some adjust easier than others. The boys are always the easiest to be excepted from what I've experienced though so hopefully it won't take long & your crew will all be playing gently & snuggling with him in no time.