This is weird because we must be seeing things differently. If this comes across wrong I am honestly sorry but can you explain how you see this as not being included?
This is a blended family so you have the core family now with the 3 teens and the newly married couple. In this nucleus everyone should be included as equally as is possible. Maddy, Caleb and Sasha for various gifts get equal quality and quantity gifts, they get equal chores, equal school expectations, equal time and attention from the new parents. Everyone is included ..if there is a dispute it is discussed and handled equally.
The issue comes up is that Maddy has an outside family ...her mom and her mom's extended family and Caleb and Sasha have an outside family her grandparents as the dad us no longer there. Unfortunately with blended families...the outside of this nucleus is not equal. One had more money, one has more attention.
As the parents within the nucleus they can ask those outside to make things equal with what they provide ....money or time, but you can't force it.
It seems they are trying to do what they can with the nucleus by requesting the grandparents to stop giving large gifts so it isn't in the face of Maddy. I am not sure what else they can do to make things equal from those outside the family and make all the kids feel heard...other than talk with them ...see how they feel and include them in the resolution.
So honestly besides the outside family as that is beyond their control how would you suggest making everyone feel included. And point out besides gifts where I made any suggestion that would make anyone in the family not feel included.