To revive this interesting and informative older thread: using one narcissism to justify another makes a little bit of sense, but more sense would be to have no narcissism at all.
Grandparents are not obligated to support their adult children. Adult children are not obligated to let themselves be controlled by their parents- EVEN if it involves the name of their grandparents (surprise!).
However, happy, healthy, family members will often consider the desires of other happy, healthy, family members to be important to them. When the members who have the desires are not happy or healthy, I think the importance to the other members go down.