The bottom two buttons on FOB are not connected. 3 is the right number for a total of 5. Those “pads” are what closes the circuit when you push the button. Clean the contacts on the circuit board, as well as the pads, carefully with an eraser. Than place the buttons on the little nips on the FOB. You can just use a little bit of vaseline or other slightly sticky substance between the pads and the rubber for the FOB. With all 5 of the membrane pads back on the rubber, place the circuit board over it and assemble the FOB in such a way that the little contact pads are always on the bottom (let gravity help you). Once it is assembled the pads are being held in place simply by the board. They got nowhere to go.
Of course, if you are in doubt use a very small amount of super glue on the rim of the contact to glue it to the “silicone button pad “