Set your remote to the same housecode A-P as the TM751 and the cams. they all need to be on the same housecode
Next set your first cam to unit 5 set your next cam to unit 6 as Brian H stated cams work in sets or groups of 4 (for Most people! I'm one that they don't)
The group of four cams work together in that when one in the group is turned on the rest in the group are suppose to be turned off automatically doesn't matter if you only have 2. The reason for setting your cams to 5 & 6 is you don't want to turn off your tm751 when switching cams and it would be in the first group of 4 with the unit code of 1.
If you press unit 1 on your remote the TM751 should make a clicking noise when it switches from on to off. Can't hear the click plug in a lamp to see if you can turn on/off
If that won't work and the tm751 is set to the same housecode as your remote then you have a bad TM751 (it happens) You have to get this step working before the cams will.