I don’t think I would have ever spotted that theme until I read about it!
I had a couple of niggles though... the superfluous apostrophe ’s’ in father’s and ‘doubles taken’ implying (to me anyway) that both doubles should be removed
Well spotted - I did the crossword last night but, as usual, completely missed the theme. I love how the Shelley's monster being split in two turns in to a homophone.