So I'm booking a flight to Amsterdam with my dad and a few friends (who are under 18, but 16+).

I'm just wondering if my dad pays for two rooms, but if he stays in one and the rest of us stay in the other, will that be permitted?

The hotel only cares the rooms are paid for and an adult signs as being responsible.

Probably, if you're travelling as a group, but better check with the hotel.

Ask the hotel.

Whyever not?