In regards to Aloe (The one that was doxxed) I'll quote and direct you to an explanation of the events as is known (This happened just before I started watching Hololive but the community was still upset about it then. Still is really)
This is a small quote from the post.
"The stream itself was around six minutes. In it, Aloe revealed to the audience that she had breached the terms of her contract with Cover Corp by accident. According to her, a Live 2D (L2D) broadcast of her testing her model out was dug up and found out by the public that happened during May of 2020. At the time, Aloe had requested permission from her manager to try out her model on a previously owned account, one that would later expose her private life to a startling degree.
The manager complied with her request and she most likely spent a while trying out the rigging of her model before finishing up. However, neither her nor her manager had actually ended that test, leaving a backdoor for people to find. It was password protected, but someone was able to find it and trace it back to her. This would lead to a multitude of doxxing attempts onto the talent. She would further go on to address rumors and the concerning amount of harassment around her."
It would be difficult for the people to not have known she was part of Hololive as everyone after the unofficial Gen 0 debuted as being part of Hololive and do so as a group in a generation.
Now as to Coco, the other person that is still receiving hate messages, the people that are still attacking her also certainly know she's part of Hololive as the reason they are sending hate messages directed at her is because she, *gasp* mentioned Taiwan when talking about statistics of what countries she gets the most viewers from. This has led to Chinese nationals seeing her very existence as an insult to them and led to the entire Chinese branch of Hololive being retired.