In English we translate an awful lot of “ha ha” and “heh heh heh” and maybe even a “ho ho” here and there, then we kick the specifics down to the visuals and voice acting. You may pull out an “ahaha”, “bwahaha”, or “muahaha” if you’re feeling ambitious, but you risk popping people’s inner monocles off if your medium is particularly literary (fortunately, this doesn’t count). In Japanese, you have a lot more leeway, as you can see here.
So basically, you’re kind of boned since FF7 doesn’t have voice acting; if you can track down the exact moment these are used, you’ll probably be best off trying to play with a sort of sync with the animation or taking advantage of the scroll speed to space things out for you. Here’s how I would handle these:
Palmer is probably a haughty “ho! ho!” kind of guy (Maybe don’t keep it at three, depending on what you have to work with; people will think of Santa Claus).
くっくっくっ is a lot like “heh heh heh” most of the time. Doesn’t have to be evil; mischievous would also do.
I’d probably handle Hojo’s クァッ クァッ クァッ！ as “Aha! Aha! Aha!” since it’s an abortive, insane kind of laughter (note that the laughs in his pre-battle dialogue are different).
ガハハハハ！ is a big, hearty laugh even if Heidegger is a villain. I might be tempted to play with this, but it’s probably best serviced with a big Brian Blessed-esque “AH HA HA HA HA!”
In contrast, particularly because Scarlet and Heidegger go together like... pestilence and famine (or something nasty like that), キャハハハハ！ is... hm, feminine. It befits an innocent girl... but also a complete bitch. It’s a bit difficult to formulate in text, but you know it when you see it.
I wouldn’t take any of these recommendations at face value; it would behoove you to see exactly where these happen in every single case. It’s not like people laugh the same way every time, even if characters in Japanese pop media do