What should I do about my parents' graves?

I think it is necessary to check with the temple or organization that manages the cemetery.
At my temple, there is an example where the bones of a deceased husband were placed in the tomb of my wife's parents' house (not adopted by a son-in-law).
I'm in the group that thinks that if the bereaved family and client are good, there will be no problem.
In terms of Buddhism, I think which one is better.
So I think it's a question of whether you care or not, and a question of whether the graveyard manager will allow it or not.

I read it.
What you're worried about is that even though your maternal grandparents did terrible things to your father, are you worried about whether it's okay to bury them in the same grave as your grandparents when your father dies?
If that is the case, I will answer.
Grandparents passed away and were guided by Buddha and God, and their ancestors greeted them kindly. Grandparents will reflect on the terrible things, bad words, and misdeeds they have committed themselves under the Buddha or God, sincerely repent, and sincerely apologize to their father and those who hurt them. Then, they changed their minds and carried on with good thoughts, words, and actions, and became pure, understood precious teachings and truths, and attained Buddhism. And from now on, they'll be gently watching over you, your father, and everyone.
I still don't know, but when my father passed away, Buddha and God guided my father, and my grandparents and ancestors kindly welcomed my father. My father has been reunited with my grandparents, and I'm sure my grandparents will sincerely apologize to my father for his misdeeds up until now. Your father will accept your grandparents' apologies and will surely forgive your grandparents.
Father will be saved from any hesitation or suffering with his grandparents and ancestors, and will attain Buddhism cleanly.
Also, along with your grandparents and ancestors, your father will warmly watch over you and everyone.
As such, anger, hatred, resentment, malice, and misdeeds disappear, and they successfully attain Buddhism without any sorrow.
So there is no problem with being buried in the same grave.
After that, it is good if the graveyard heir agrees and permission from the manager is granted.
I sincerely pray to the Buddha, gods, ancestors, and grandparents that your father will continue to be blessed with good relationships with everyone and live every day richly, and that everyone will continue to be considerate of each other and live a happy life.
Also, when my father lives a full life, the Buddha or God always guides me, and I sincerely pray to the Buddha, God, ancestors, and grandparents so that my grandparents and ancestors would warmly welcome my father. Shishin Gassho Nanmu Amida Buddha Namu Amidabutsu

First, in Buddhist teachings, a “tomb” is not a “place where the soul resides,” but is positioned as a “place where people with a relationship hold memorial services.” The essence of a deceased person is not confined to a tombstone, but rather returned to the legal world and is present everywhere. Therefore, “who you enter the same grave with” itself does not determine the nature of the deceased.

However, people prepare their minds through “form.” My father used to have a relationship with my grandparents where he had a deep conflict, and it's natural to wonder “how about entering the mother's grave together” from that memory. What is important here is to prepare a “shape where the late father can sleep peacefully” and at the same time “a shape where the family left behind can put their hands together with peace of mind.”

The term “shukuen (shukuen)” is used in the Shingon sect. Encounters and family relationships are all connected in a flow of cause and effect. The feud with my grandparents is also part of my father's life, and beyond that work (), the current family exists. Entering a tomb together can also be an opportunity to use that past causation as a “place of reconciliation.”

On the other hand, if your heart doesn't fit in any way, there's no need to force them to go into the same tomb. Choosing a different shape, such as an ossuary or permanent memorial tomb, is also a splendid Buddhist choice. The important thing is to choose “a path where those left behind can make a memorial service without regrets.” No matter where the tomb is located, memorial services can be delivered by chanting sutras and offering thoughts.

As a conclusion
When parents enter the “same grave,” it can also be a relationship where past causal relationships turn into “reconciliation”

If there is strong resistance, it is Buddhist correct to choose “another tomb or ossuary”

Above all, preparing a “form where those left behind can pray peacefully” is the memorial service itself

Please don't be too bound by the shape of a “grave,” and may your family choose a place where they can sincerely put their hands together.
Gassho

At one point, a parishioner named Mr. A came to consult with me. Mr. A's wife had a serious illness a few years ago, and her illness progressed and her life expectancy was short. After discussing preparations for the funeral, Mr. A decided that he wanted to prepare a separate grave for his wife in addition to his ancestral graves.

Mr. A: “My wife wasn't on good terms with her deceased mother. When the two were together, they had constant quarrels. I'm worried that if I go to the same grave as my mother who passed away, they're likely to fight again. It's a pity that they suffered from illness for years, passed away, and on top of that, they fought at the grave again. When I think they'll fight even after they die, I think it would be better to keep their graves separate.”
Chief priest “Mr. A, let's think calmly about what would happen if we built a tomb just like you wanted to do it for you. When you say you build a separate grave for your wife, you're leaving the conflict between the daughter-in-law and mother-in-law in the form of a grave, right? I wonder what your children and grandchildren would think if you left it that way.”
Mr. A “...” (said, taken aback)
The chief priest “If you leave the conflict between your daughter-in-law and mother-in-law in the form of a grave, how would your daughter or grandson feel when praying at such a grave? The conflict between the daughter-in-law and mother-in-law will be engraved in the hearts of the children and grandchildren. Building another grave will be at your own expense, and it will also be a burden for your daughters.”
Mr. A: “Certainly, maybe.”
Chief priest “I understand the feeling that makes you want to worry that disagreements, grudges, and bitterness during your lifetime will continue in that world. But that is a shallow idea for those of us who live in a lost world called this world. Mr. A's parents became devotees to the Buddha, received a feudal commandment from the indigenous people, and left for the Buddha's world. And I'm undergoing training in the Buddhist world. My wife also becomes a Buddha disciple when she passes away and goes to the Buddha's world. The people who became disciples of the Buddha overcome a dispute between their daughter-in-law and mother-in-law. I became a Buddhist disciple and practiced Buddhism. It's a misunderstanding to think that the people who became disciples of the Buddha are in conflict with their daughter-in-law and mother-in-law in the afterlife.”

When I think back to when I was alive, I'm at a loss. I understand how you feel. But while rude, I think this is a shallow thought. The reason I received the sacred name at the funeral was because I pledged to submit to the Buddhist ball and swore that I would keep the Buddha's precepts.