You should be able to make it a double chest if you crouch, look at the side of the other chest, and place the second one. If that doesn't work, try placing a block behind where you are placing the chests and then looking at that block to place the chests (without crouching this time).
You should be able to make it a double chest if you crouch, look at the side of the other chest, and place the second one. If that doesn't work, try placing a block behind where you are placing the chests and then looking at that block to place the chests (without crouching this time).