Well, there are some problems with the count of needed people for some Grandbosses - that's true!
Antharas isn't that hard - LastResortHell killed him about 8-9 days ago with 1 Cardinal, 3 Spoiler, 1 Doombringer, 1 Phoenix Knight, 1 Shilien Templar...
Weapon were most Vesper out of my Kamael with a Vorpal Ancient Sword (without SA at this time) and Skull Edge duals on 1 Spoiler!
Armors were half to half Vesper and Vorpal - 1 Spoiler on Vorpal Light, 1 Doombringer Vorpal Light and the Shilien Templar on Vorpal Heavy
It is not impossible - I had to Dualbox my Kamael and my Dark Elf Knight, the others played single box!
Vesper Weapons on +12 are strong enough and my Armors are "only" +12