Opinions inbound! Keep in mind I'm biased because... In the Pitt, I played an founding character who eventually became a leader (Ninazu) and currently play the leader (Vale). Also, for the CotC, I played a founding character and once-leader (Ninazu). And for the Typhoon, I played a founding character and longtime-sometimes HP (Rosemary). And for the Palm Glades, I played the son of the original leader and a HP (Quasar).

I think a merger between Palm Glades and Typhoon makes more sense, because (1) they share similar ideals and (2) are already strong allies. They are different in some ways (ei the way the Palm Glades views powers and their usage as somewhat frivolous while Typhoon embraces powers), but I think those differences would be more plot-points rather than pain-points, if that makes sense?

I also think a merger between CotC and the Pitt would possibly work, but wouldn't necessary work well. While both groups are "evil" in alignment, their morals are very different--I see the Pitt as chaotic evil with an emphasis on the chaotic, while CotC is more neutral evil with an emphasis on "keeping it all in the family." In addition to the other cons Orion listed, both groups view loyalty very differently; the Pitt believes in-fighting is the best way to survive (except during Gael's reign), while family bonds are a founding reason for why the CotC exists.

While a part of me would love to see a "Pinkie and the Brain" scenario with Vale and Romulus leading a merged Pitt-Cotc, I think a merger between the two groups would destroy the culture of what makes these two groups unique.