The problem seems to me that your team is very underleveled. Like sumwun suggested, get the Diglett to level 41. Don't let it evolve, as then you would have to wait until level 51. Whenever it tries to evolve, mash B (in case you don't know) to stop it. But when it does learn Earthquake, let it evolve, as Dugtrio's speed will be very handy. Be careful against his Weezing and Koffings, as Ground type moves have NO effect on them. I'm saying all this in case you're not experienced with Pokémon at all. A Psychic type would be best for this gym, as Psychic type moves are super effective against all of his Pokémon. A good Psychic type at this point is Kadabra. It's fast and has super effective STAB like Confusion. I hope I helped!