well u can get a better fire type like a darmanitan. get darumaka by trading a measly luvdisc @ Apophyll Academy.
Darmanitan have super power at lvl 47 and decent fire type moves. plus it has sheer force ability which awesome and he has decent speed too.
hmm well i would break the field to make it easier. And the perfect person to do it is Quagsire. yes quagsire is slow but it can least take some ice hits due to its water typing so u wont get 1 shotted. Quagsire also learn EQ at lvl 35 and u can find them at azurine island at round lvl 30-35. u might also consider a camerupt a decent fire and ground which also has EQ but not so early at lvl 50 i think but yeah i will still stick with quagsire easy to find easy, learns Eq fast easy to train just spam kill the marcargo at mt pyronus.
here is what i would do:
Lead with Quagsire. EQ the field if quagsire can kill the first pokemon bannett/serra send out good if not just let it die as it did its job of getting rid of the field.send in fire type to beat bannett team and send in moxie jolly scarfty to beat serra team. if cant beat the 3X lvl 50 pangoro than get a hariyama to beat serra or get a darmanitan to kill 2 birds with 1 stone since darmanitan has super power which is a decent fighting type atk.