My suggestion on this regard is to give 2 different MG nests to the Engineer 1’s and Engineer 2’s.
As engineer 1, you get the standard MG nest as you would on the current engineer 2 squad.
As Engineer 2, you get that standard MG nest type but with a window of sandbags around it as part of the structure, and a little bit more durability on the gun.
The smaller MG nests definitely have less firepower than HMGs, but do have a couple small advantages:
They take up less room, so you can use them in tighter spaces (Moscow Campaign especially has some very good locations where MG nests fit, but HMG does not.)
They are more accurate and easier to control.
They have a slightly less noticeable tracer effect than the HMG, making them less likely to be targeted by aircraft.
With that said, I definitely hold to my suggestion and giving different MG nest structures to the different engineer squads. This includes being able to place both of them independent of each other for build restrictions. (Essentially if you have both squads equipped, you can put down one of EACH gun placement. For a total of 2.)
Also as a sidenote, they need to make it where you can see both on the map and also an indicator when nearby. This way teammates can find their way to the mounted guns more easily.
All MG nests should be available only for MG squads. We don’t need engineer to be all-rounder squad, they all already must have class. Every special structures should belong only to specific squads. AT cannon should be available only for AT squads etc.
Engineer squad should be able to build only support structures. For example rally points could be buildable only by them. And come up with more buff-like structures. Something like passive slow healing to nearby allies (but this could be only for medic squads). Maybe ammo boxes could be buildable only by engineers.