I thought the big mum was living through her daughter, forcing her to do the things she wasn't doing herself. It was quite telling that when she wasn't allowed to become involved in the music lesson she had nothing else to do. Time to get a life methinks!
The 'posh' mum gave herself away when she described the music tutor as "the most expensive and he has a W1 address." Shows what is important to her, silly woman! In that family I felt sorry for the other daughter who was constantly told she wasn't worth the time and effort and she wasn't as special as the singing sister, that was truly awful and shame on the parents for allowing that. I imagine the singing sister will find herself ostracised from her siblings later on if she doesn't loose the little madam attitude.