From top to bottom, looks like an original M60, the M60E3 (if so, the first time since TOP made one), the M60E4 in MK43 Mod 0 flavour, and the M60E4 in MK43 Mod 1 flavour. Although looks like they are opting to not reproduce the authentic modern Mod 1 top cover and are yet again going with the older style cover with a rail bolted on.
LCT used to make M60's but they've been OOP for a while, so this must be a reboot.
Lambda Defence did make a teaser post about an M60E6 conversion earlier this year, but it was quite a while ago and nothing since.