This node will get elements from a Link Instance given the instance object and a Category. It also reports a ‘coordinate transform’ for the Link Instance itself.
You also have the option to simply pick the linked instance with the “Select Model Element” node:
This checks if a given Point is contained inside a Revit Room element. Combined with various collection tools, it can effectively build a list of items that are inside a Room across links in a federated model.
DYN sample: Elements in Room – Multilink and Multicategory (DynamoWorks)
Dynamo Nodes 