Date Difference between two tables that have another table linking them

I need to calculate the difference between "Request [DATETIMEINT]" and "Workorder [INITIATEDATE]"

the tables are linked through a third table that matches the Request ID from the Request Table and the WorkOrder ID from the Workorder table and connects them via the ActivityLink table.

I've tried to add a column and do the datediff but I can never seem to get both the request table and the workorder table.