Help me understand 101

I’m really struggling understanding this .30cal LMG gang. Why is there third guy and what is his function (where is that explained). If I lose loader, there is penalty but what happens if this third one dies?

They can have rifles?

I just bought 3rd edition rulebook but I just can’t find anything.

Oh, and is this LMG now part of basic airborne team in 3rd?

So frustrating!