Complex sentence: Maddie takes more private lessons than the other girls, and is very clearly Abby's favorite athough the mums are clearly not happy that Abby shows favouriteism they just seem to accept it, knowing they cannot change her opinion.
Split into simpler sentences: Maddie takes more private lessons than the other girls, and is very clearly Abby's favorite. The moms all are aware of the blatant favoritism that Abby shows to Maddie and get upset about it, but at this point seem to just accept it, knowing they cannot change her opinion.