There is currently no option to do either of these:
Email tracking (opens, clicks, and replies) get thrown off when you copy your email to your teammate. If they open or reply to it, it'll mark it as opened or replied under Interseller. This is because there's no way to differentiate who is who since the same email was sent to two different people. We also don't recommend copying a teammate via BCC for the same reasons. BCC is intended for copying emails to your integration or CRM.
What you can do instead:
If you work in a "pod" like team where you'd like to receive replies and reply on behalf of your teammate, we'd recommend using a tool like Front so you can collaborate on each other's email inboxes.
Note: Forwarding emails will also throw off email tracking so we don't recommend this either.