Interesting that you're doing a rewatch! I thought about rewatching the first series when it was recently repeated, but didn't.

I think it was all the build-up - that moment where Alison and most of the ghosts thought they'd got away with the patch-up job on Dante and clearing up, without taking account of Mike. And of course, it was how everything came together in the 'punchline'.

How the downstairs ghosts all came together against Julian fed into the theme of family in what Alison first said to Thomas.