I'd argue the cats, even though they are lower level than the Balor, are able to compete with one far better than they should. 2-3 cats could easily take a balor, which is supposed to be a cr 20 monster- and that primarily has to do with the mutant felines regen ability- like their stats being high is one thing, but the regen basically can turn one cat into an utte r brick wall if you arn't built to hit them often. The balor could probably kill a cat by meteor swarming and then stabbing one to death, but the other 2 cats would regen by the time cat 1 dies.. and have a good shot at killing the balor if it doesn't bring out more spells. (Which it would do in table top, but ya know how nwn is)
So my suggestion is- tone down the cats AC or their regen, you can't have both imo- or attach their regen ability to their rage ability.
to emphasize why this kind of needs to happen, imagine a level 14 martial character- over leveled for the cr 11 cat with minimal wards. Let's say they get ac 40ish and.. BAB 27 (14 + 7 str + 3 from feats + 3 from weapon enchantment)- You can't beat the cat in a straight up damage contest reliably because the cats BAB is still way higher than yours, and your only hitting on a 15 or better on ONE attack per turn, and you can't out endure it via expertise because the cat regens.
