To add what was already said by others: To fight large number of orc warriors you need two things to begin with:
-Good brothers. Not just 11 level brothers but good 11 level brothers. You need brothers with 80+ attack and 20+ melee defense at last. More the better.
-Really good armor. 200 armor will not do, you need 300 armors. For this you of course need brothers with high stamina, so back to first point.
Once you have that-
Few good shields. Along with tanky brothers with shield mastery and high melee defense (and underdog). You want these to tie up as many of enemy as possible while your polearms and 2H concentrates on one or two at the time. They have to be able to stand 3-5 turns against 2-3 orc warriors without getting serious damage.
Don’t bring too many spears. Spears don’t do enough damage for this kind of fight. At most 2 dedicated tanks on the flanks who will help prevent enemy from overwhelming your flanks. Just don’t count on them to hold flanks indefinitely, expect them to just buy you time.
2H warhamers. Having 2 good brothers with 2H warhamers gang on the single orc warrior will wreak his armor in just one turn, leaving him open to polearms and axes. While 1H hammers looks good on paper against orc warriors, I did not found them to be very useful in reality. Their base damage is just too insufficient to deal with orc armor.
Ranged units are useful to thin berserks and young orcs before they reach your line, but are almost useless against warriors. If you bring ranged in to the battle, they should be hybrids which can switch to polearms and long axes once orc warriors get close.
Some useful perks to have are:
Overwhelm -especially on the 1H tanks. Orc warriors have low initiative and overwhelm works well to lower their chance to inflict damage. This perk also work well against undead, they too tend to have low initiative (you have to act before enemy you’re attacking in the current turn for overwhelm to work).
Fearsome -orcs doesn’t have high resolve and making them panic is one of the easiest ways to fight. Unfortunately this perk doesn’t work at all against undead so think before taking it.