Step sons mom wants me to send him with my boys to their cousins sleepover Update

My boys are going to spend the night with their cousin for a 4 day sleepover. My step sons mom asked me if I could send my step son too because he's never been away from home and she wants to finally make friends. My step son doesn't want to go because he's never been away from. Also the boys at the sleepover are 14 and 15 and he's 12. I just don't see him having a good time especially when he doesn't want to go. I told her I can just hang out with him while the kids are at the sleepover since he doesn't want to go but she said no. He needs to go and interact with boys his age. The boys are teenagers.. He's a preteen. My cousin is fine with him going but he has anxiety and I don't want to force him to do something he doesn't want to do. My cousin lives an hour and half away too...

Update: Well I knew this was a bad idea. I took him over there and told him I was gonna stay for a while and it he decides he doesn't want to stay that's fine. He mainly sat on the couch and when I was getting ready to leave he said he wanted to stay. I asked if he was sure and he said yes so I went home. Well I get a call from him crying. He said he was scared and the only reason he said yes was because his mom told him he had to and he needed to stop being a baby. He told me he tried to call her to pick him up but she won't. I told him I would call her so I did and she told me he's being a baby and her son needs to grow a pair, that it's not that big of a deal. So I may have crossed some boundaries, but I went to pick him up. He was really upset and crying wanting to come home. I'll take the heat from his mom but obviously he wasn't ready for this so I'm not gonna torture him.