It has had a huge impact on me (the middle child and only girl). Because all of my parent's attention, emotional and financial support was funneled towards my brother, I was forced to be hyper-independent from a very young age. It worked out well as far as me being the only child of the three of us (the men are always favored in my family but that's a whole other thing) that is successful, stable, and financially independent. But, I also struggle with knowing that my parents have always placed my brothers' needs above my own, even when they are unreasonable or even damaging and toxic.
I truly believe that had they cut the cord and forced him to take responsibility for his behavior and actions, he would be in a much different place today. he would have cursed their name for a few years but eventually realized it was for his own good.
As a final aside, one of my mentors had a son like your daughter/my brother. He kicked him out around 20 years old and didn't hear from him for a few years. During that time his son had cleaned up his act and enlisted. They are extremely close now and even run a fly fishing tourism company together.