It's unfortunate that when your neighbours complained two nights ago, you didn't contact your guests straight away to remind them of your house rules rather than waiting till last night.
You say you contacted them last night. Well they have obviously ignored your request to keep noise to a minimum and not party, by disturbing your neighbours again last night.
I do hope you made sure as well as talking to them you followed it up with a message via BNB confirming if there was another incident they would be asked to leave.
I think rather than waiting to call your guests, you need to call BNB. Let them know that your neighbours have been complaining of partying two nights in a row and that your guests ignored your request yesterday to keep the noise down and partied to the early hours and that your neighbours have been complaining.
Tell BNB you need them to cancel the booking - be firm on this. Don't cancel as someone advised or they will give you strict penalties.
BNB will then contact your guests.
Taking a party of 6 young people was always like to result in some sort of party, so be more careful of the guests you accept and talk to them about their plans before accepting any booking.
Next time you must be more prompt in your actions. It is not fair that your neighbours should suffer for two nights in a row because you are making money from letting out your property. I would make sure you apologise to your neighbours, assure them you are taking actions to get your guests removed today and make sure you send them a gift - flowers, chocolate, a food hamper - whatever you think they might like with a handwritten card of apology.
Good luck and let us know how it goes.