How to set up a chat in youtrack customer and developer?

Question

Project management

Advice needed
I need to set up a chat in youtrack to communicate
Add an employee and a customer
So that the customer sees only those performers. who is in the project *internal / external user) I
did not see other participants and users
And it was possible to control the transfer of data and texts in this group / conversation
to set tasks, etc.
Tk is a project in progress
And questions often arise
Skype thought. But we don't want to. To have direct contact with the customer