Each make of remote has their own receiver. So no, you cannot combine gate and garage onto any of your two remotes.
But you fit a universal receiver into the garage or the gate, which will then accept the odd remote to work on that opener.

Now if you have two garage doors, you may then fit a 2 channel Universal receiver into the garage, which will then operate both doors on any of your existing remotes plus your gate.
So all your existing remotes will work on both garage and gate.

Two things are possible here. Firstly your remote battery maybe running low.  To check this, press and hold the button down, the led must remain solid. If the LED flashes, your battery is low.
Replace the battery.

If all remotes are reacting the same way, you will have to delete all the remotes in your receiver, when relearning each remote into the receiver, stand 20 meters or more away. This strengthens  you receivers reception. All remotes should work at least 40 meters away.