Quick questions -- will Evil Racist Berserker Elder Brother be attacking alone, or with a group? If it's with a group, what will the composition (roughly) be? E.g., will it be him, the death knight, and a bunch of mooks; him and a bunch of mooks; or something else? Are they going to have the chance to plan some tactics for their attack?
Is his hatred so extreme as to be irrational? Is he a macho or (nominally) honorable type of guy -- the kind that wants to fight the most dangerous foe?
If so, I would have him plan the attacks so that goons/others tie up the other members of the party (especially the cleric), while he personally focuses on obliterating the lead abomination (i.e., the elf). If you can, arrange for the sorcerer to be near the paladin at the start of the fight. Then ERBEB can try to verbally urge the sorcerer to "come to his senses", "join us", and otherwise get his Vader-recruiting-Luke on. Once the sorcerer firmly rebuffs the recruitment efforts (by, say, saving the elf, or blasting ERBEB with the biggest spell possible), the ERBEB should go totally berserk, screw the plan, and attack his traitorous brother.
They may even want to try some less-lethal means of trying to take out the humans (e.g., tanglefoot bags, hold spells, silence spells, etc.), just in case the humans can be persuaded to come around, and also to allow them to focus on all the unholy inhumans (who happen to include all the solid warrior-types).
The less extreme his hatred, the less their tactics should be warped towards the non-humans, and the less irrational the ERBEB should be. OTOH, the fact that they do genuinely hate non-humans should have some effect on their tactics, and it should be possible for someone to taunt the berserker ERBEB into less-than-brilliant tactics. 'Cause that would be fun.
