Patsy that is so sad. Although I have witnessed such families where the parents favour one child over the others. Personally I cannot get my head around that. You have kids which should be loved equally. You've created these beings who all have different personalities, and if parents are too thick to understand this when they embark on parent hood then they should have thought hard before starting a family.
The agony columns are full of adult kids recounting the lack of love and attention from their parents while a sibling has copped for the lot. My Dad used to criticise my younger brother a lot (well he was a bit of a sod), but I would rigorously defend him and my other brother, as I didn't want him growing up and have the feeling of being 'left out', we were all equal in my eyes, and I wasn't having any of it when Dad started kicking off.