To be completely clear:
- homework  and coding challenges are on-topic.
- Issues with tags should be edited, it's rare to get questions with perfect tags - I get them wrong all the time too.
This means the questions are on-topic and so we shouldn't close the questions.
TL;DR: It's recommended to ignore who the user is, but ultimately it's your choice to vote, comment and answer however and whoever you want.
In general, what does that leave?
This situation doesn't warrant flags.
You can vote however you want. You can up-vote off-topic questions and down-vote perfect questions. I wouldn't recommend doing either of these, but you have the privilege to do so.
If you feel this is something that warrants no votes then you're allowed to not up-vote it. Same for down-votes.
It's normally recommended to vote on the quality of the post, not the user. And so some may disagree with your opinion if you change it because of the user. But these users have their own vote buttons that they can use.
Some people think down-votes should include a comment. If you decide to alter your vote because of this then you may want to post a comment.
This can be mutually beneficial. The user stops vexing you, whilst getting more up-votes.
Some users may ignore your comment, or become argumentative. If they do either I would recommend you leave them be. Nothing good will come from arguing or trying to persuade them to your side.
Answers are entirely optional. Like voting it's recommended to ignore who the user is, as these benefit more than just the poster. But we can't exactly hold a gun to your head, and force you to answer.
For this specific thing, there shouldn't be a site policy. This is as the act of posting two questions at the same time isn't necessarily bad.
If I had limited internet access then I may download challenges for offline use, and post my solutions when I next get internet access. These challenges may have nothing in common with each other, and so there may be little overlap between answers. Punishing someone in this situation seems overly hostile.
However if someone posts two very similar solutions to two very similar problems, then answers may be very similar. IMO this wastes the time of our answerer's, which I wouldn't encourage (upvote/answer).
And so vote, comment and answer in ways you think will benefit Code Review.