They do not take any damage from other npc or player but take dmg from fire or blast.
1.12.2

It is well known issue and it doesnt work on pirate versions

is there a fix ?

Zwasco - This is due to the user having a pirated or cracked version of Minecraft / and or the T-Launcher. This is not our problem and dont expect any sympathy. The NPCs take their hostility stance from the owner, and if the owner doesn’t have a UUID as pirated copies don’t, then they have no hostility to anything. So they won’t attack or be hurt by anything. This is not a bug, its not something we need to fix or worry about - buy a copy of the game cheapskate!