49 damage from Harpy, what the hell

Hello there,

2nd playthrough (Tactical) after a just finished one (Medium).

I Went to the beach, near Mol's friend, battle started, and after Astarion move (1st battle move), Tav was one shot (struck down) by an Harpy ; 24 + 25

All my characters are lv3 and about 27-29hp

Also hit (not damage) dice said 12 on a 1d20 but still crited twice = ???

2nd Harpy killed the boy, and 3rd Harpy nearly landed to kill Tav

All of that in turn 1, without the possibility to handle anything

All but Astarion were charmed

Also on turn 2, Astarion couldn't Rakish Sneak Attack, tooltip said I have already used my action point despite the fact my action point and bonus action point was available ; 1st time it happens in this game. Can someone explain this also ?

I don't remember the Harpy battle was that hard

How do you handle this battle on Honor mode ?