So I saw a couple overhaul patches for 3 and 4 fixing various bugs, which is really amazing. Has anyone found a way yet to make Erana and Katrina marriable by any class? Maybe with patches or mods?

I get the logic of the game, but I find the restriction rather lame. Erana says a fighter is too stupid and a thief too dishonest, but this is an RPG for Coles's sake, you can have a fighter with maxed intelligence or a thief with maxed honour. Same with Katrina and her "paladins are too good for me" nonsense. I wasn't too good when I sacrificed myself to get you out of hell, or when *spoilers happened* last game, why does that matter now?

What makes more sense, I think, and what I'd love to see, would be the marriage conditions tied to the character attributes rather than their class. Communication for Nawar, Strength for Elsa, Honour for Erana and Intelligence for Katrina (I know she would take a "dumb" fighter but I think int makes the most sense for her character). That's more reflective of the type of character you're running than their class.

Anyway, I'm replaying the series for like the 50th time and getting close to 5, has anyone found a workaround for this in the last 25 years?

QFG5 rolled Communication into the Honour stat for some reason, so your idea wouldn't work 100%. (I know QFG4 didn't use the stat at all, but still!) And Elsa cares a bit about honour too, she might be a thief, but she's not a murderer, and if you go slitting the throats of unconscious guards, she won't like you much at all.

As for the reason Erana and Katrina are class-locked (also stat-locked, I think they check if you have Lockpicking, not if you're a Thief), it's because Devon actually has a different personality based on his class. The fact that he's a mostly-silent protagonist makes it hard to notice, but the Fighter is rough and a bit bloodthirsty, the Thief is shifty and manipulative, the Wizard is wise and measured, and the Paladin is chivalrous and noble. This doesn't depend on player input at all - it's canon for the classes and is reflected in how each class gains points. Killing monsters is good for every class, but it's only a scoring action for the Fighter for example.

The official novelisation goes into some detail too: interestingly, the Thief originally wanted to be a locksmith, and got caught practicing on his aunt's wine cellar - everyone in Willowsby got the wrong idea and ran the poor guy out of town: he became a thief in order to survive, and eventually became a hardened criminal.

I don't have a proper answer for the OP, but I want to echo the sentiment; I think the game's marriage restrictions are silly. Katrina + the Paladin in particular makes sense to me. The Paladin is not entirely a "lawful good" bore - in fact, he's willing to break the law and do whatever it takes to create the greatest good for all. This seems like a key distinction between the QFG Paladin and the D&D one.

Also, Katrina has become a good guy by QFG V, so pairing her with the Paladin would be the next step of a perfectly sensible character arc. Lastly - the Paladin is (to me) easily the best character type to play in QFGIV - so it's frustrating that you can't marry Katrina in the sequel.

I suppose Erana not wanting to marry a Thief is the only restriction that makes sense, but even that seems unnecessary.

Another thought - a mod should make it easier to marry Erana and Katrina. The ideal gifts for them are too hard to find, and you shouldn't be penalized for not speaking to them immediately after leaving Hades.