Searching all the achievement, i found this one called "The Brother" that can be unlocked after defeating Esdras but after I defeat him, the achievement still gets locked. I saw videos on YT and the only thing I need to do is kill him, but again, it can't be unlocked

That's strange, maybe it got broken with one of the last updates/expansions? I don't know but maybe it's the case.

On the very first version it worked and unlocked fine. Have you tried to do it on a new saveslot, beating him and see if it unlocks? Also now in the current version, there is an achievement menu... see if you have it unlocked there or not.

That's good to hear - maybe OP was just super unlucky then. Still it would be of interest to me to know whether he has that achievement unlocked at least in the main menu. Second thing I wonder is whether beating the Sister during that fight has any impact on it - imo it shouldn't have, but who knows. Cheers!

Thanks for your answers. Searching in the main menu achievements, I actually got it unlocked. So I don't know why it doesn't appears in my progress since I beat the game twice. Maybe it's just a bug or something