L.C.
Just role play... it's easy.
Tell him what you are going to do and why. You tell him that you will be him and he will be Danny...
Then just do what he does. Then ask him how it feels to be Danny.
3 is a bad number no matter the age. I'd not schedule play time for the 3 together - only 2 or 4 for a while... So - you'll either have to find another friend or just have 2 kids at a time.
That said -- there is no better teacher than the peer group for this sort of thing. They learn it faster and better from their friends -- "if I'm mean, my friend won't want to play with me. If I want to spend time with him, I'd better suck it up and be nice."
LBC