Paul's email client (or his web-based email service) won't receive Peter's email address in the header that's attached to your email. So it will be totally impossible for Paul's client (or email service) to send anything to Peter since, as far as his client/service is concerned, Peter doesn't even exist.
Similarly, both Peter and Paul won't receive any 'reply all' mail from either Janet or John, because Janet and John will not received have Peter's & Paul's email addresses in the header attached to your email.
Janet & John (and, of course, you) will get Paul's reply because (since they weren't in the Bcc section) their addresses will be in the header that Paul received. You only need to forward Paul's reply to Peter.
That, of course, assumes that Paul actually uses 'Reply All', instead of just 'Reply' anyway. The way to check is to examine the header of the mail you receive from him, as that will show all the addresses that its been sent to.