I a going to be making fondant decorations grapes, cross, bread, etc for a first communion to use as cupcake decorations since when can I make the grapes etc. ??????????? And how to store it?????

If you want them to remain somewhat soft, then make them within a day or 2 and store in a barely closed cardboard box.

If you want them hard, you can make them weeks in advance and store them the same way.