Okay

well according to the source i read, they will be purified by the ML also so they won't hurt the FL when she's using them

Wait, but the butterflies can still be used as weapons, right? If so, let’s goooo

well im not really sure but there's a spoiler source that the fl use it to kill her father tho
I guess the purification just erase the butterflies' feeding to fl poisonous blood so the fl doesn't need to feed the butterfly and drink poison also