I understand banding and a band being blocked by a single creature. The creature is considered blocking every creature in the band. However lets say I have Gruul War Chant and attack with a band including Quagmire Lamprey. One creature is blocked by 2 creatures are both creatures considered blocking all the other creatures? I am assuming they are.
If one creature in an attacking band becomes blocked by one or several creatures, every other creature in that band becomes blocked by those same blocking creatures (C.R. 702.21h). Thus, Quagmire Lamprey's ability can trigger once for each such blocking creature in this case (C.R. 603.2c, 603.2).
Just in case…
Do note that if some creatures of the band have Menace but some others don't, the whole band can still be blocked by a single creature. The same is true for all 'evasion' abilities: if some creatures have flying and some don't, a non-flying creature can block the whole band.
702.21h If an attacking creature becomes blocked by a creature, each other creature in the same band as the attacking creature becomes blocked by that same blocking creature.
Example: A player attacks with a band consisting of a creature with flying and a creature with swampwalk. The defending player, who controls a Swamp, can block the flying creature if able. If they do, then the creature with swampwalk will also become blocked by the blocking creature(s).
EDIT (Oct. 21): Correctness edit.
Do note that if some creatures of the band have Menace but some others don't, the whole band can still be blocked by a single creature. The same is true for all 'evasion' abilities: if some creatures have flying and some don't, a non-flying creature can block the whole band.
Example: A player attacks with a band consisting of a creature with flying and a creature with swampwalk. The defending player, who controls a Swamp, can block the flying creature if able. If they do, then the creature with swampwalk will also become blocked by the blocking creature(s).
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules