How to save your own families grave stones?

Well first... You really can't save it. Once the sim is dead that's the spot the grave stone appears. You can go into build mode and use the hand icon to move it. I'm pretty sure you can't read who's stone is who's though. You can't put it into your inventory. If you move and save the game afterwards, the gravestones are lost forever. If you move but don't save you can quit and then go back to where you last saved the game. If one of your sim dies and they are the only sim in the house your game is over. I don't know is you can go back before your sim died. If you have two sims is the house and one dies quit, then go back into the game and your sim should be living. Just don't save it after they die or then they're forever dead. If you accidentally kill your sim and save, then you can just make a new sim and have them move in and then re-position the sim and pretend the original one never died and the sim you just made is the original one. That's what I would do.