The only way you can save their stuff would be to place it out in the open in either a room, and save the room to your library, or just save the whole house depending on what you want to do. Don't have anything in any type of things you can store stuff in, that won't save. (Bookshelves, refrigerator, or any other type of storage item) All their stuff can then be quickly put back into their inventory in the new game save after you put it down on the new lot in the new game save. If money is an issue, you can first place it down, enter the freerealestate cheat, and then move your new sim in. There are other money cheats you can use to adjust the amount they currently have in their household funds. This way if you want you can also give them what they currently have in their household funds in your old game save if you so choose.
