My brother's char has slightly higher initiative than my character, and wolves must have a higher initiative than my character but less than my brothers.
What level / stats? Or just in general, how far back do you usually get placed in combat?
I tried a witch/witch and witch/wayfarer combination, and they worked as expected at the start of the game (up to level 2), with the second summon always added after the first. I never had 2 characters with Summon Wolf in earlier builds, but then even at higher levels the wolf always went after the caster (with the same main character initiative, a summon by the first can be placed after the second).
If I delay my turn, though, the second wolf gets placed after the first one, rather than after the caster (and using the undead swordsman scroll places it in the same position, between two opponents, it would have if summoned earlier).