You seem to be doing a lot of weird things. Why are you importing the common sub machine guns file there? That is not something you need outside of the motion tree files. Also, smg_mp44 is deprecated, you should be using the newer model. Finally, there are a lot of weapon models in the west_german folder, you should be using those instead.
Try this:
model =
{
"../../../common/newmotiontree.abp",
"../../../common/engineer.abp",
"../../weapons/west_german_rifle_kar98/west_german_rifle_kar98",
"../../weapons/west_german_rifle_g43_sniper/west_german_rifle_g43_sniper",
"../../weapons/west_german_smg_mp40/west_german_smg_mp40",
"../../weapons/smg_mp44_default/smg_mp44_default",
"../../weapons/west_german_panzerfaust_100/west_german_panzerfaust_100",
-- Main Mesh
"volksgrenadier",
}
Note: I suggest using / instead of \ because you don't have to escape it (\\). Makes it easier to read and less error-prone.
Make sure the animator field of the entity_blueprint_ext in the ebps matches this .abp file AND make sure that the .abp file is in the
exact same folder structure as the original.
If all else fails, use the included Archive Viewer in the Mod Builder to make sure your .sga file has the .abp files in it.
Edit: The only time you should edit either of the motion trees is if you want the weapon to be a slot item.