There is only one M240G MG (GPMG) carried atop the LAV-25. It is in a scissor mount that is mounted on teh commander’s side, but can be swing and used by the loader as well. You can see it below.
There are 2 M240G MGs missing from the Trumpeter kit. The other is the barrel for the coaxial MG that sticks out of the hole to the right of the main gun. You can see it on the first pic above. Check Prime Portal for more LAV pics. That is where I found the above pics.
This is of course if you want to model a modern day LAV. The mount that comes with model was used into the mid-90’s. Also, the original machine gun used on the mount (circa late 1980’s) was the M60-E3.