Gentle Giantesses

It could be a good idea. And what you said may have been caused by a kind of curse on Jak and Blake, made by some other villains (if Blaze, he'd use weird lab pheromones on them to alter their behavior).

Other idea was that it was only one universe. Joana, Blake, Jak and Jasmine encounter somehow with unknown enemies (to each other):

Example:

Jak and Jasmine encounter with Blaze, who had previously allied with Nostory and attacked them, Blake appeared to stop him by a firce fight and barely made it. Then they met.

If not (I'm not familiarized with your story, and correct me if I'm wrong):

Nostory and/or Seth appear, after saying some things like they were going to destroy them, they attack Blake and Joana, he fights back but is overwhelmed by the demons' power, and loses. They're saved in the last moment by Shadow (the good demon, you know) and then Jak and Jasmine appear...

Just an idea.

EDIT: By the way. Your love problems' storyline it could be a good one, but, since I know my characters, some things don't match in their behavior: Blake would have to be under somethings' effect to cheat on Joana, and she, more than angry would be sad or heartbroken, and at least, the first she'd try it would be to get Blake back. (Not a criticism, if you want to go with this idea I don't mind)