Trying to justify portable repeaters is a very hard thing to get done.
Especially on itinerate channels!
I have a mobile vehicular repeater that can cross-band and in-band to licensed repeaters. The vehicular repeater runs in simplex so the portables don’t need to do anything special to use it. If it leaves the scene, the portables still all work together, but without the link to the larger system. That’s just licensed MO6 (mobiles only private carrier) and is hardwired to the XG100M, which either cross-bands to the trunking network, or in-bands to an FB6 repeater.
Unless everyone in your party gets a ham ticket or you install a lot of commercial infrastructure and license accordingly, you’re not gonna be able to cross band.
GMRS sounds like the best fit for you. It allows the family to use your license. It allows repeaters and higher power mobiles, and you can use it for non-business related comms.
-B