There is a soul after death, and the soul will be reincarnated according to the good and evil done before death. Killing animals, stealing, fornication and hurting others are all bad things, while cherishing life (releasing), chanting scriptures and helping others are all good things.
Six divisions in the wheel of karma: heaven, man, Asura, beast, hungry ghost and hell. This is what the Buddha said, but it was not created by the Buddha. The Buddha just told us the truth of life in the universe, let us do good deeds and accumulate virtue, and let us be reincarnated in a good place.
I hope you can understand Buddhism. "Buddhism" is the Buddha's education to all beings in the nine dharma circles, telling us everything.
If you want your grandparents to be good in the afterlife, recite the scriptures and Buddha, set them free, and return their merits to them.
Amitabha, I hope your grandparents can have a good life.