I get on well with my older brother but my relationship with my younger sister isn't great.
I do think maybe our parents did contribute to that.
Me and my brother always helped out on holidays/round the house e.g. with washing up. Both got part time jobs at around 14 and pretty much paid for our own leisure activities. My brother didn't want to go to college but got a job straight from school and joined the military one year later -he has had a very good career. I went to 6th form/uni, funded myself and also have a good job.
Our sister was never expected to help, seemed to be allowed to do whatever she wanted, including being really quite nasty. Was always paid for so never worked as a teen. She did get a job on leaving school but was sacked after 6 months because she rarely turned up. Parents continued to fund her after.
It's still the same now. She has two children and still depends on my parents for a lot - money, food, kids uniforms etc. Whereas me and my brother sort ourselves. If it was a case of her being unable it might be different but it isn't.
I only have one DS and tbh, part of my reasons for not having another are based on my experience of siblings