Charles is correct that this requires programming. I've prepared a sample template that works, which you can download from my site at https://jay-freedman.info/TaskLists.zip .
When you unzip the template TaskList.dotm, go into its Properties dialog and check the Unblock box. Then save the file in your Templates folder, and double-click it to create a document containing copies of the tables in your post. Add some task names in the first table, and then open any of the combo boxes in the second table. The combo boxes will all contain the same list of tasks from the first table.
Open the macro editor and double-click the ThisDocument module in the TaskList project to examine the code. The comments explain each step in the macro, but be sure to ask here about anything that's confusing.