I have a two door, two car garage, thus I have two garage door openers with two remotes. Lets refer to them as door A and remote A, and door B and remote B. They are three button remotes consisting of one large button and two smaller buttons. I want the large button on remote A to operate door A and one of the smaller buttons to operate door B. Naturally, I also want the large button on remote B to operate door B and one of its smaller buttons to operate door A.

I can get the large button to operate the respective door. Howerer, when I try to program the smaller button from the other remote, it overwrites the programming of the originally programmed remote. At that point the only remote button that will open said door is the smaller button. What am I doing wrong and how do I make it work the way I want it to work?