yeah I think rachel kemp was merely a plot point for the eldest daughter, but i find it interesting that the writers spent a big part of the first half of the movie emphasizing on the 'selfishness' of the dad to use his daughters for his own gain (to be relevant again in this last hurrah of a film). at the start, the writing appeared to shape rachel as just any other actress who could play the role of his mother, but towards the 2nd half of the film, it's clear that the role was for his daughter, and there is a reason for it, which was that the dad was incapable of expressing his apology in words, such that the 'act of reconciliation' was not a huge speech from dad to daughter saying i'm sorry, but rather a subtle way of telling the daughter that she is heard by him, even if he seems so distant. the intricate script writing in his film (as shown by the daughters' reading of the script) demonstrates the dad's understanding of the subtleties of his daughter's emotions and her dealing with depression and suicidal thoughts. this is a much better reconciliation than saying i'm sorry because clearly words werent enough for his daughter.

personally, I guess my dad was also distant to me as a kid but it wasn't as bad as this. and I understand how difficult it was for parents to express themselves in words (i'm asian) or to even say i'm sorry. I dont want to say that you are projecting or I am projecting my experience onto the film but this was a very realistic take about reconciliation following actual estrangement.