Hi!
1) this is by design and since it’s a channel meeting they cannot access the chat since it’s stored in that teams-channels conversation area!
Nothing to do here afaik
2) if you are referring to a meeting with 2 channel, you can’t! I’d suggest creating a normal private meeting and invite all attendees manually here!
For any request about features go here:
https://microsoftteams.uservoice.com/Adam