Ok, I have this problem, I'll try to explain it :
I used to work on several novel(a)s at the same time, more a curse (not able to focus) than an aptitude.
Regulary I find that an idea, a subplot, a paragraph (or just a good sentence sometimes) could fit in two stories. It works well on each, offering good possibilities of developing the charachters, storylines... etc.
And from there comes the dilemma : I have to make a choice, so I spend several days or weeks, changing my mind, hesitating, making me feel like I'm Buridan's ass !
I don't expect a miraculous answer, but if you already had the same problem, It would be good to share experience.
Thanks.
I would concentrate on one novel. and develop your characters. Victoria is to use the term, Character-led. Novels have to be Character-Driven.
Though, do be careful. Developed characters take on a life of their own and will lead you off on tangents if you don't keep a firm hold on them.
Charlotte Bronte - 'The writer who possesses the creative gift owns something of which he is not always master.'
In that situation I would ask my characters, but then I take the term 'character led' a bit far!