Two vexing questions: the Weasley twins and Sirius' mirror

I've run myself aground on two questions and they're paralysing me. They're stopping me from my usual free-flow of thinking around the Harry Potter books and films and, therefore, blocking me from posting to this blog.

The two questions are:

1. Did J.K. write the characters of Fred and George Weasley in such a way that she's made them clearly different individuals or was she content simply to present them as one person in two bodies?

2. Why didn't Harry use Sirius' mirror to contact him at the end of The Order of the Phoenix, rather than allowing himself to be lured into the trap at the Ministry?

I've talked a little bit about the first question in earlier posts and it still vexes me. I will have to find the time to review all seven books, chart the descriptions and dialogue for each of the twins and see what I come up with. I can't think of any other way to answer the question. The problem is finding the time.

With regard to the second question, my colleague who is currently reading the books for the first time raised it recently as we were talking about how different the fifth book is from the fifth film. She said it really bothered her that Harry didn't just use the mirror to check on Sirius -- after all, Sirius must have had it with him when he was caring for Buckbeak and not available to Harry through the fireplace.

I have to admit: that issue never bothered me because, in the numerous times I read the novel, I never really registered the mirror and its importance when Sirius first gave it to Harry. It wasn't in my mind as I read the remainder of the book.

But my colleague saw all the films several times before reading the novels so the mirror, which is so vividly depicted in the film versions of the seventh novel, remains strongly in her memory as she reads.

I write all this here for two reasons: in hopes that, by writing about these two questions that have been othering me, I'll clear them from my mind and allow myself to think of other Potter-related things and in order to spur myself into action to pursue both questions on the coming long weekend.

What are your thoughts? Do you think of Fred and George as seperate entities or just two names for a single character? Does it bother you that Harry failed to use the mirror to check on Sirius?