my father is religious, I’m not and I don’t care what happens to my body after I die. Burn me, use me to feed stray cats.
To me, wasting money to buy a plot of land so I may be buried with them when I die is a stupid idea.
It is, however, his money. Who am I to disagree with him?
Are any of your siblings married or have SOs? Most people in the US prefer to be buried with their spouse than their parents. At least in any graveyard I’ve been too, that’s how it is.
Maybe tell him, it’s a waste of money if it’s only going to be him and your mother buried there.