From this dream, we can know that your grandparents' love for you from childhood is in place, and you can get comfort and protection from them when you are injured as a child. This kind of protection even exceeds your parents, and you can feel your grandparents' unconditional tolerance and care for you. They will never refuse you (their door lock is always open, and I can go in at any time in case of danger).
Now the meaning of grandparents in your dream is a kind of love, a kind of tolerance and a sense of security. When your heart is hurt, you are looking for this kind of love, tolerance and security to calm your heart. Grandparents have become your image symbols.
I suggest you look at the interpretation of Zhu Jianjun's dream. These theories are introduced in detail in his book.