Sibling Environments

I've been thinking a lot about the differences in environment for Big and Little Whompers. Big Whompers, as a babe, never had an older sibling knock her over, poke her, love her ferociously. Little Whompers has Big Whompers, a force to be reckoned with, someone to contend with, someone to adore. These two will shape each other, that is obvious already. But I am a different mother to Little Whompers than I was to Big Whompers, and that is my biggest concern.
When Big Whompers was a baby I wasn't trying to parent a toddler. Now I am. Despite my best efforts not to embody my mother and yell at little provocation, I yell a whole lot more than I would like. And there is a pent up aggression that never reared it's ugly head when Big Whompers was a baby. I didn't have the frustration of trying to protect my baby from another of my own children. The conflict of "Mother Bear" who will do anything to keep her baby safe...but what if it is her own (other) baby who is the threat?
There will be so much more frustration, and anger, and yelling for Little Whompers babyhood. I look back at my childhood now and wonder if therein lies the broad distinction between my brother and I - his rebellious aggressive childhood compared with my straight-laced easygoing eager-to-please self. I always wondered how two children with the same parents could come out so differently - but I realize now that the parents are not the same, they are shaped by the first child, and their interactions with the first permeate the environment to the second.
Did the stress on my mother's psyche as a result of parenting me set the course for the aggressive (yet surprisingly close) relationship between her and my brother? And why is it that I, who had the benefit of her to myself during my formative years, cannot seem to interact with my mother on a less hostile basis? And my biggest concern - what do these interactions mean for the relationships I have with my daughters as they grow?