Combining remotes it not always as simple as buying a new remote that can operate two types of doors. When purchasing a new remote you must check the brand and model of your motor, the frequency and the model of the remote and most often all of these must match to ensure the new remote will work.
In most cases, homes have two different motors installed at different times that use different remotes and you will end up having to carry two or three remotes with you at all times. The most effective way to use one remote for all motors is to add a receiver on one of your motors to match the other.
We recommend to have a receiver installed by a garage installer as some motors are not as straight forward as others. To put it simply, the receiver is a small box that be connect to Motor A and will allow the remotes that control Motor B to be programmed into the receiver and control Motor A. All of your original remotes will still continue to work on motor A but will still only control Motor A. Motor B's remote will now be able to control both motors.