Can we add other members to the Slack channel and reply customer directly?

Can we add other members to the Slack channel and reply customer directly?

Yes, you can add other members to the Slack channel and reply to customer inquiries by default.
If you would like to only allow the agent who picked the ticket to reply to the customer in the private Slack channel, you could toggle on the "1 on 1 Live Chat in the platform of your Slack channel.