2. Engineers were using several SMGs at least per Squad, Sapper usage would be the most approriate I guess.
-> If Devs don't want the Soviet "Engineers" in Divisions/Brigades to reduce Fortifications ...since they may not have had Satchels, de-mining equipment and so on, (like Assault Sappers do), just create a Light Infantry Squad (or any Type of Squad) which in return just call "Battalion Sapper" (or whatever) but since not being Type "Engineer" not reducing fortifications. This would be a good compromise and not make Squads with SMGs and SA-Rifles into Labour Squads with Mosins.
If someone could provide more Sources regarding Soviet OBs/TOEs I'd appreciate getting them.