Sorry for my late reply. But I was trying to make this solution work with my data. So the solution you gave me works perfectly fine as long as there are no double (Min([creation date]) . In my case, most of the time, I will have several Min([creation date]) for a same AncestorID.
So what Qlik does, is to leave [Min Responsible] blank because several solutions are possible. So I was trying to use Concat to have my [Min Responsible] with all the possible values.
Or, other option, is to force Qlik to pick the first value possible. So, if I have several responsible at a same (Min([creation date]), I want to pick at least one value (doesn't matter wich one).