Uhm. Doxxing is actually illegal so don't even think of that, alright? Telling this for safety.
As of mass reporting, depends, if you do it all you then it can be considered a moderation abuse, so they can use it against you. But just giving proper insight of this situation helps people find out about this and all together make an effective report.
Unfortunately inside the legal terms not much can be done if YT's automated system is flawed.
Also yes I saw that... And also they're most likely a cyber bully too... Yikes...