How to initiate flow in one Dynamic 365 instance from another Dynamics 365 instance?

1. How to initiate flow in one Dynamic 365 instance from another Dynamics 365 instance? 2. How to initiate Power Automate flow using Http request? 3. How to remove user's roles in an instance (and trigerred from another instance)? 4. How to get records using FetchXML in Power Automate Flow? 5. How to disassociate (or associate) relationship records in Power Automate Flow?