How can you block few ppl at once?
It's hard at first, but you'll get the hang of it. Players rarely, if ever, coordinate their strikes, and for some reason they often end up 2*pi/n out of phase--maybe they love rhythm--and with not much room for more than three players (n=3), there's plenty of time--especially when you consider that the guy in the middle can only stab or swing overhead, and occasionally the same is true for the edge players. (This is one reason I prefer to fight alongside a wall or fence if I'm caught defending against more than one person.) If you're lucky and they hit each other--you can usually see this coming before the hit actually lands--your gamble for smacking one of them is actually pretty safe. This is, to me, the primary advantage of the speed of the two-handed stab when you're in group fights.
The major exception to the phase delay is a large group of enemies chasing you because you are separated from your group. (Perhaps they have already gone to hell, and you are the last one standing.) Then the enemies tend to swing wildly and without regard for teammates' well-being.