No, the forward offset rails would interfere with the Strike Industries VOA M-Lok Forend.
The Aimtech Warhammer Shotgun Mount can fit your Huglu Atrox Standard Shotgun, but some slight modification may be required as it is a clone of the 870.
The manufacturer states that this Aimtech Warhammer Shotgun Mount Remington 870 is only compatible with Remington 870 12 gauge shotguns. I am unaware of an insert that will allow it to work with a Remington 7615 Rifle. I recommend contacting Aimtech in regards to compatibility with that rifle.
The Aimtech Warhammer Shotgun Mount Remington 870 Black ASM-2WH may not fit with a magazine tube extension do to the forward barrel clamp not being able to fit between them. However, I recommend contacting the manufacturer to confirm.
This features over 20 inches of picatinny top rail.
Yes, this will be compatible with an 18.5" barrel and the Magpul MOE forend.
You will need MPN: ASM-2WHX which can be found here: https://www.opticsplanet.com/aimtech-warhammer-x-series-tactical-full-length-rail-mount.html?_iv_code=A9-T8-WRMX-ASM-2WHX
Yes, this is compatible with the Tac-14.
The 20 gauge model can be found here: https://www.opticsplanet.com/aimtech-war-hammer-tactical-rail-mount-rem-870-20ga-lt-blk.html