There's a simple way to fix Trunks and Goten, GIVE THEM THEIR OWN THING! Trunks already has the sword stuff from Future Trunks, so let's get started on that already, have them become unique fighters with a specific skill, for Goten bring back the power pole, develop a fighting style with that, have them both reach SS2 and become some sort of a defense/sparring team mentored by Gohan and Piccolo. That way you can leave pure power to Goku and Vegeta, potential with Gohan, tactical to Piccolo, and skill based fighting with Trunks and Goten.
The smartest thing they could do right now is for Goku and Vegeta to belittle them two again after the tournament. This will hopefully annoy them enough to sneak into the hyperbolic time chamber for a couple of years. They come out SSJ2 and have actually physically matured.
It's not hard at all to write that in. But out of the z-warriors, I think only the main three are going to stay relevant.