Hello @Claire262
Sorry this happened to you as a new host.
They were only able to do this because you accepted their ammended booking. I wouldn't have.
You can't control neighbours having noisy parties. Rather than ammending their booking they should have contacted you and you could perhaps offered flowers or a bottle of wine.
Nor can you control mosiquitos although if you are in an area where they are prolific in your guest book you should mention this and perhaps provide mosquito repellant plug ins.
If you are not familiar with how Airbnb works, I would snooze (put your listing on hold) while you learn more about how Airbnb works. The help section on their website, the community guides here and the new host tips will help you.