Without money, can I dig my grandparents' graves and bury them together?

You cannot be buried together. The so-called joint burial is limited to living couples. They can be buried together in a grave, but they can be buried next to the ancestral grave, and they must be the next one, not the first one. This is exquisite, and we can't mess around and bury our grandparents and grandchildren together. This is just a custom in our local countryside. That's called going out for three miles. The rural customs in various places are unknown in other places.