I must admit I'm not a big fan of diplomas anymore. I keep one of two and delete/give away the others. If some are relevant for a family in that generation, I keep them until that person dies. After that, I often throw it away. You can also get those WA chests to put them away, too.
Regarding the ghosts, another lot-graveyard is the best idea. I often remove the tombstones without ghosts at the local cemitery to add some of mine, but in general, I don't bother and I let them resting in the mausoleum (if I ever play long enough, actually).