The Twins normally do about 50-70 damage per hit, and the max defense you can have in the game is roughly 80. This means you'll take at least 10 damage from their weakest attacks. They also have a damaging DoT too.
So I placed a Hellstone. It deals 20 damage on contact unless you have an obsidian item to negate it. We hooked on the Hellstone to negate the knockback effect of being hit, and since our defense was well over 40, we only took 1 damage per tick. Since you have some invincibility after being hit, we can't be hit by the boss, as the instant the invincibility wears off, we are hit by the Hellstone again for a measly 1 damage. Far more preferable than the boss hits, even if we're constantly taking it. We have the luxury of just shooting at nearly still bosses too. We added a ring of regen and cross necklace to slow the health deterioration. Philosopher stones were safety nets, and Star Cloaks for free DPS since we're always being hit anyway.