You can't press them like that and get equal pressure on each , the top one will get almost twice the psi as the two bottom ones.

The top one would get the full weight of the press , the bottom two would get the full weight of the press , plus the weight of the top cheese , divided by two.

So if top cheese weighs 4 pounds , and press weight is 10 pounds , top cheese gets 10 pounds pressure , bottom two get 14 pounds divided by two , which is 7 pounds each , or 30% less than the top one.

You need a board that will span all three at once without too much flex , a piece of 2 x 12 maybe.