I've been trying to fight the twins with both MEAC and calamity, and some other mods. Retinazer works fine, but when Spazmatism dashes, it just sticks to my character and i can't do anything to evade and i just instantly die. I think the problem is that calamity itself changes the bosses' AI and it's incompatible with MEAC's changes. I also had some issues with BoC, which just despawns just a few seconds after being summoned.
I've run into these issues while playing with some friends in a world with both mods, but not when i played by myself in a world without calamity. I still haven't tried the reworked EoL.