This sounds like the perfect use case for trigger conditions. You can read about trigger conditions at Power Automate Trigger Conditions made EASY - Power Platform Community (microsoft.com). You can then set it up so the flow only runs if the three tasks are no. You will probably also want to add you Concluded column to the task list so you can add that as a trigger. Otherwise the workflow will run again if the task is edited and the three tasks are still tagged as completed.