I have a similar problem:
I switched to the Goth family after playing another family for a while. By that time Mortimer was a young adult, both his parents dead and their graves nowhere to be found. They are not in the mausoleum either. I figure graves only stay there for a little while because otherwise the thing would be cramped in no time.
My question:
Is there a way to force spawn graves or any other way to get hold of those ghosts?
Because I'd really like them back...