No, its def not that he "just doesnt like you", he is scared and unsure, and I think you know that. its just frustrating trying to get a child comfortable in a "new" place. especially when you are compeating with Mom's one-on-one raising! it will take him a while, I wouldnt push him, I wouldnt try to hold him too much or get too close right now. I would make sure all the kids play with him but give him proper space during play, he may be overwhelmed and will def need some time to adjust, he has never done anything like this before, its all new to him! i would make sure to keep a solid schedule and ask Mom to drop off quick and painless. as a matter of fact, ask her to give a kiss before coming in the door, then open the door, say "I love you" and hand him over and walk away, the longer the linger, the longer the pain!!!! I'll bet he will end up one of the best kids you'll have, just need to give him time.
Did you ask Mom "what things make him happy?" like rolling a ball back and forth? or playing with blocks? alot of times you can choose those things the child enjoys at home and sit on floor (even across the floor from him with that item and allow him to "come to you") will probly take only a few minutes to show interest and then he will move in to "check it out". I find, it takes "mammas babies" a little longer to learn to trust, but after that..they become the sweetest little creatures!!!

no wonder you are having another issue at nap time, you have ALOT on your hands right now!!! Hold on...in another couple months you'll be flyin high!!!!!