My parents have two daughters, my sister and I, but no son. After our sisters got married and had children, my parents also made them grandparents.
It is normal to call grandparents in our local area, because basically every family has two daughters, so everyone acquiesces in a new culture.
Sister married close, just like the custom and culture of brother-in-law's family, naturally called grandparents, adults and the elderly all agree with each other, calling each other grandparents Mo Grandma Fan Grandma.
But I'm harder. My husband's family is seriously patriarchal. There is no such thing.
Later, I also communicated with my husband many times about the differences in local culture, so that he could understand my parents' thoughts and expectations, and it was also our blessing to give the elderly a place of peace of mind. Later, my husband gradually agreed, and we also taught our children to call the old people on both sides grandparents.
But my in-laws still disagree, which is not allowed according to local customs. I can only comfort them that you are grandparents and will not change, and please don't mind the child's name. After all, it is also a blessing for children to have one more grandparents who love children.
Finally, it was solved harmoniously.
These things, such as culture, cannot be changed by personal strength and time, and we need to moisten them slowly. Even if you can't, don't insist and respect the most traditional culture.
The most important thing is family harmony and a happy life.