I have not got to the grenzers ingame yet, but they were historically equipped with double barreled muskets (one barrel rifled) and short pikes (to stabilise heavy musket and for self-defense). But only 2500 pieces of these "Doppelstutzen" were made and issued to grenzer sharpshooters. The weapon was used from 1768 to 1808, AFAIK.

So it is historical weapon, but in the same sense as flaming pigs and screeching women...

Concerning skins and realistic uniform details, I could gladly help with my limited knowledge of uniformology. I have my copy of Bleckwenn´s Frederickian uniforms ready