From the sounds of it your cats are stressed out probaly as you are packing things in boxes to move. It might help to get some feilway plug inns and put rescue remedy in there water. Also get a couple more litter trays {golden rule one tray per cat plus one}. Personally I think this is a problem you are going to have until you move and they get settled into there new place.
Remember Cats never ever go to toilet outside the tray to make you cross they do it because something in the world has gone wrong and they are stressed out by it and messing is there way of telling you.
good luck

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