How to counter a squad of 2 L and 1 M?

My friends and I are testing some different comps and we have been having the most success running 1M 1L and 1H. We can deal with basically any comp until last night we ran into a squad that had 2 invisible Lights 1 with shotgun and 1 with pistol. The M was their healer.

Their level of coordination was impressive. They'd cloak and ambush me first. My friend runs heavy with a flamethrower and he couldn't do anything. They'd appear out of nowhere and kill him before he could react. My other buddy would simply die since they were together.

I tried swapping to sonars, but in the middle of the chaos it was hard to focus them down. The only thing I haven't tried is the glitch trap which I think would force their cloak and abilities out if I bait them into a room. Any ideas on how to deal with this comp as a M? Taking feedback for the other classes too.