After twins reach level 141, they are still useful for some campaign stages. They just need to be able to survive for a few seconds at the start of the fight. They will connect your frontline heroes, so that they share a percentage of their attack and defense rating which other. This is really powerful with a your carry and a tank like lucius in the front row.  And this Connection  persists even when the twins die.

Extremely OP with the right equipment and Ascended. They die quickly because a sister always goes in front and gets her first dmg (It's not like Rowan or Mehira, which you leave as Elite in the back, without them taking any damage, and do the job done ).

How good are the twins at mythic? They die insanely fast at legendary+. I’m on 24-56 but am thinking they could be strong in pvp.

How good are twins?