Here are some options you could use, depending on the context:
* A generation: This is a broad term that encompasses both sets of grandparents.
* A family: This is a more general term that could include all generations of a family.
* A pair: This is appropriate when referring to a specific set of grandparents (e.g., "The pair of grandparents were very proud of their grandchildren").
You could also get creative and use a more descriptive term:
* A gathering of grandparents
* A group of elders
* A tribe of grandparents
Ultimately, the best term depends on the specific situation and your desired effect.