rickye, your last sentence is entirely correct, and contains everything you need to solve this puzzle.
If you look at the eight extra words from the down clues, you will see that their lengths in clue order follows a distinct thematic sequence , and they can also all precede the same significant 6-letter word.
Regarding 23D, there is an Irish royal connection.
Finally, one of the main stars of the sit com used to be Good, but isn't so nice in this one.
Hope that gets your little grey cells firing....