I'm not sure what changes you've made to them, but they completely swept my team. I felt completely in control of all the battles up until then, in fact I felt more than powerful enough and those two just stomped me blatantly. I think a big problem was that fern never sends in a replacement making the fight 1v2. The other problem is that they can attack each pokemon you send in as a replacement, it's incredibly difficult to fight a 1v2 when every single pokemon you send in gets hurt before they even get a turn. I'm not sure what stats those two have, but they found difficult to damage with my wartortle (being evolved and a higher level) only doing about 1/3-2/5 of Magby's health with a watergun and they did a tremendous amount of damage back to me. I think if either Fern actually helped in the fight or if they were toned down so that you weren't fighting an uphill battle it'd be a bit more reasonable.