Well you can go with multiple reasons. You can use the route I used. Where they sealed the soul of the Kyuubi into Naruto and the chakra of the Nine tails into the other children, so Minato and Kushina would train the ones with power and ignore the one with the useless burden.
Or you can use the route where Minato or also Kushina are being manipulated by an outside force, like someone controlling them with a genjutsu.
Or one with the shinigami. So instead of Minato paying with his soul for the sealing, he and his family lose the love they have for Naruto.
It’s a good summary but what does two in one here mean? And I’ll give you a tip. Make sure your chapters aren’t too short. That’s annoying. I’ve seen a lot of fanfics with great ideas and stuff but the execution is crap, like too short chapters and other reasons.
Well good luck.