I see it as developing different relationships and being complementary to each other
Over the years our DDiL's mother has become a dear friend. She lives a couple of miles from DS and family, and we live 200 miles away. She was there when the DGC were little, but we have been able o do different things with them, having them to stay on their own, for up to a week, taking thm places and doing things with them that the other grandmother did not do. DGD is good needlewoman because Itught her to sew.
So do not see yourself as a secondary grandmother. See yourself as a complementary grandmother. Perhaps while the DGC are tiny your companion grandmother will see more of them, but, wih the right attitude you will be able to find ways of developing your relationship with your grandchildren doing things your companion grandmother does not do.
You could discuss the issue with your son and DiL, but life ain't perfect. We wished we lived closer to our only grandchildren and could have seen more of them - the first flies off to university this autumn, but thats life.