No, they cannot.
Combats in Numenera move quickly enough that a GM should not hesitate to use large groups of creatures as challenges for PCs, particularly powerful PCs. A screaming, squirming horde of thirty abhumans is a possible encounter. A swarm of fifty laaks could also be used.
To make things easier, the GM can take any creature and have a group of six to ten of them attack en masse as a single creature that is two levels higher, inflicting double the original creature’s normal damage. So thirty level 3 abhumans might attack as five level 5 mobs.
No. You are six individuals with different stats, weapons and damage, because the rules for mob requires that the grouped creatures to be the same type. You cannot combine different creatures into a mob then take the highest or lowest damage between them to apply.
And again, because it says the GM can, not that the players can. So allowing this or not is completely within the GM's hands. But you will have trouble figuring the attack rolls and damage done.
Yes, if all six of you are exact copies of each other (can be done with artifacts). However, this requires GM permission, as the mob rules (quoted above) are within a GM-only chapter (creatures)..
Yes, if you, as an individual character, somehow obtained control of a group of creatures (also possible with artifacts), you could control them as a mob with GM permission.