It seems a shame to live life arranged on a spread sheet, but families are SO complicated these days.
A young couple with children will probably visit one set of grandparents on 25th and the other set on 26th. Often the couple will alternate that over the years.
Many grandparents could make the same arrangements for visiting their gc.
The major problem is when there is a distance to cover, in which case it becomes a question of xmas vs new year, which can also be alternated over the years, and might even make it esier if there is more than one set of gc to be visited for each gp.