The family head can score any match played by their family members. However, those matches do not show up in My matches - only your personal matches show there.
So you need to navigate to the tournament or league to which the match belongs. The easiest way to do this is via the Explorer feature - accessible as the first item on the main menu drop down.
From there you can choose Events and then drill down (possibly having to choose your club section and sport) to get a list of all active tournaments and leagues. Just choose the event in question and you'll get the draw.
With the draw on screen you can click where your match is and the match details will then be shown allowing you to score the match.