Not all failed but mostly one among the siblings is more popular...Raj, Shammi and Shashi had been successful siblings (in the past)... Sunny and Bobby Deol (although not their half-sibling Esha)... Pooja and Alia also have only the same father, Ishan and Shahid, too (they grew up separately).
One would have to make a survey among the respective siblings/families for the why, I suppose.
SRK's sister had started her studies when the father died...Shehnaz got ill and her mental health deteriorated even more after the mother died...since then she lives with SRK.
9