[Esel Mann]

I suspect there is more to the riddle which is missing. The reason being, the riddle as it is written in the post does in fact have multiple possible answers. Usually a riddle is supposed to only have one answer. No? The fact that three reasonable as well as possible answers come to mind and which are:

- the barber has no hair and thus does not need to shave;

- the barber has hair but does not shave or have shaved the hair;

- the barber shaves, as the "all those" encompasses all or everyone. the and thereafter merely adds another set which is meaninless;

suggests that there are one or more constraints missing from the riddle.