OK, so this is more or less a version of the early Brotherhood of Evil Mutants vs the New 52 Justice League.
The original Brotherhood's membership is slightly altered: it includes Magneto, Scarlet Witch, Quicksilver, Mastermind, Toad, Blob, and Unus the Untouchable.
The Justice League is Superman, Batman, Wonder Woman, Green Lantern (Hal), Cyborg, Aquaman, and Flash (Barry).
While this is an early Brotherhood team roster, the members are mostly at their current levels:
--Magneto, Quicksilver, and Toad are current.
--Scarlet Witch is as she appears in Children's Crusade (at least this is my guess at her power level in CC): she has her magical abilities plus her hex power. She does NOT have her HOM power level.
--Unus has his original power set from before his first death.
--Mastermind is at his most powerful from when he was alive.
--Blob has his normal power set.
Since the Justice League comic has not been out for long, we may have to speculate a bit on their power levels. You can use any feats or infer any abilities from either the Justice League comic or their individual comics. In the case of Cyborg, who I think hasn't appeared yet, use his Flashpoint power levels.
No initial speedblitzing. The Brotherhood has time to put up whatever shields they want ahead of time.
The Brotherhood has a basic knowledge of the Justice League. The Justice League does not have any information about the Brotherhood.
Morals off for the Brotherhood, and morals on for the Justice League.
The fight takes place in the middle of Metropolis. Fight begins at 50'.
Win through death, KO, or incapacitation.
[Blob's powers edited; Brotherhood shield situation edited]