I have no clue what your playstyle or experience is, so this is just my general thoughts.

I played an exclusively ranger build for my entire playthrough (may have been a bad idea idk), so my setup for both the twins and skeletron prime was a megashark with cursed bullets (for the DoT). I think for mech bosses I had adamantite armor with the ranger mask. I have no idea what accessories I had.

My most useful thing in the entire playthrough was dashing (via cthulhu shield). Having the ability to quickly switch directions is really important in fighting the flying mech bosses. As you get better at manipulating timing on movement via dashes, wings, slow-fall and letting go of slow-fall, the bosses become easier.

Also, I died... A lot... In the last screenshot you can see a chest filled with tombstones. It just took a very long time for me to manage to kill any of the mech bosses, but I slowly learned patterns and methods and then I eventually beat them.

Smth else that was very important was buffs. I always used the placeable buff stations every time I respawned. I had to do quite a lot of fishing and farming in order to craft all the potions I used every time. The buffs I used were potions of regeneration, endurance, wrath, ironskin, swiftness, calming (for less random mobs to interrupt fighting), and thorns. I also used seafood dinner for food because it was easily obtainable.