The ‘mystery bad guys’ seem to have at least two different firearms: a ‘grenade launcher’ and an ‘assault rifle.’ Screencaps & analysis below the jump:
The grenade launcher:
I suspect this is built on an airsoft grenade launcher, the Ares B&T GL-06:
The details on the end of the receiver and stock seem to match, though it is possible it is an earlier version than the one pictured. Additionally, mounted on top of the grenade launcher, but upside down and with the handle removed (?) is an Ares SCAR grenade launcher:
The ‘assault rifles:’
I do not know what if anything these are based on. I suspect they may be largely made from scratch, as the panel lines on the stock and receiver strike me as suspicious.