A trigger node would be the trigger for the workflow to start, so of course you can only have one being used at the same time. If you have multiple that can work but it will only trigger with one of them.
You can simply use an HTTP request node to retrieve the data you need.
Or if you need to actually retrieve that data with a webhook sent from somewhere, you would need to have a seperate workflow that receives those webhooks and save the data into a tool like baserow, to be used with your main workflow that retrieves calendly triggers.
Depending on which call happens first. If the Calendly call happens always first you could use the Wait-Node.
So Calendly Trigger would start the workflow, and it would then continue once the special URL of the Wait-Node got called.