How to do your own thing in someone else's lead?

Question

Bitrix24

In our business process, two or more employees can work on a lead. That is, there is only one employee responsible for the lead, but other employees can do actions on it. We have a real estate agency and, for example, any other broker can show an object by agreement with the person responsible for the lead.
In the standard functionality, you can invite any participant to the discussion. But, apart from how to write in the chat, he can do nothing. And it is necessary that the actions of this auxiliary employee are also reflected in his history of actions for the weekly report.
There are many cases of this kind, and as a result, a person does not have his own leads, and he has done a lot of work for other employees as a help.