You can, but if you use Shulk and Fiora's kids and their gang...ask me first. Ricky and Vio actually have some buddies in their homeworld their age or close because of course the band of seven heroes...well, once there was peace and it was safe, after a dangerous war, there's bound to be a baby boom.
To add something, I'm thinking of adding a Link kid. Female. She'll be quite young in the current timeline, like too young to fight, but eventually I can do a situation like Lucina's time travel. She's fascinated by any advanced tech...and finds nerds adorable, so she kinda crushes on Rickson a bit. It's not just his nerdiness that she finds cute, she also likes his stormy gray eyes and small rounded homs ears. Add some drama there because of course she can't have him. Rules against crossworld romances and crossworld crossbreeding.