Mandalf did not spawn in heart of gold lvl 4, so impossible to get the achievment kill all the family members.
The cutscene started showing mandalf but then he did not spawn anywhere on the entire map so I was unable to get the achievement that requires killing all family members of the duke
Game Version:
Steam Public
Platform:
Windows
What I've seen, you have to kill every family member, and the duke at the end.
So kill his wife first.
If it still happens, please let us know