Won’t say the position I am but in any family, would you think it’s ok for parents of adult children to go on holiday with each of their kids/grandkids separately?
So Greece with DD, SIL & DGC in the spring
and Spain with DS, DIL and DGC in the autumn?
Someone thinks that spreading the time is unfair and it would make more sense to go just once or even twice with everyone but DD and DS in the situation do not particularly get on and the families are quite different.