There are already drawbacks to having more than one companion on reservation (no one is eligible for C+/FC upgrades with more than one companion on same reservation). I used companion cert for spouse and one kid (companion certs are transferable) and used RUCs to upgrade them (you can now use RUCs for companions on separate reservations as long as on same flight) , and used another companion cert for myself and other kid (and are thus comp C+/FC upgrade eligible).