So - Donna's mum is not definitely dead, although it's heavily implied that she is. (They could mean she may as well be dead because she never turns up) & The whole strict Catholic/performer thing can be overlooked.
Young Harry does turn up to the island, with guitar and no longer wearing a Sid Viscious shirt (they got that right).
Bill's great aunt is Sophia, the woman who runs the pub, and lets Donna stay in her old farmhouse for no rent. Donna looks after her when she's older & gets left the farmhouse.
The timeline just about works if you take the starting date as late 90s, when the musical was written.
My questions: Where did Sophie go to school? Donna had no money so surely Sophie went to school locally, but she's best friends with an English and a Scottish girl. Where did they meet? Sophie's only 20 in MM1, so not at uni (unless she dropped out because she met Sky?)
If making the old farmhouse a swanky hotel was Donna's dream, why didn't she do it? Presumably the money cam from architect Sam, and they had 4 years after MM1 when they could have started the work.
MM2 doesn't have the same exuberance as the first movie. The older actors don't have to prove anything & can afford to show everyone just how bad their singing is (and they do!). The younger actors are still needing to establish themselves so have to play their roles straight. I loved how much Colin Firth seemed to be laughing out loud at just how ridiculous the entire thing was.