I once played a ghost family. It was more than a year ago, so things may have changed and my memory is maybe not so good.
My playable Sims behaved just like others. The born-in-game ghost kids would go to school normally, age normally... Really I don't think there was anything different with that family, besides the obvious: they are transparent like ghosts, haunt randomly do do haunting sounds, and they carry the grave mark in their inventory.
The only thing I'm unsure is about accidental death. Could they die "again" from electrocution if they have the color from an electrocuted ghost for instance? Have you tested this Chronic?