Help With Disrespectful Horse?

My horse 8, half Arab half qh gilding, is disrespectful to me when I am riding and especially when other people are riding him. When I'm just leading him, he is very respectful and does anything I ask. When I have other people ride him, he just won't move for them so I lead him. When I lead him with other people on his back, he pins his ears and tries to go faster than I want him to. He jumps up and paws the ground. He also tries to nip and every time they ride him he never pays attention to me. He is always looking someplace else. It's almost the same as when I'm riding him. I can get him to move but when I do, he swishes his tail , jumps forward and pins his ears. I try to correct him but he doesn't listen. It gets frustrating! And like I said before I have no problem with him on the ground. He is calm, quiet, and pays attention to me. He never stares off into the distance. I lounge him just fine to. The trainer I had up here before said it all fit properly and the vet said he was perfectly healthy. I know it's not his problem, it's me not knowing how to treat a horse while on his back. He thinks he can get away with it all. Also please don't suggest that I get a trainer up here because money is tight these days you know. Any way thanks!