Siblings

I went to a friend's wedding right after I got out of graduate school. It was a moving and beautiful weekend. What I witnessed profoundly changed how I viewed sibling relationships. I had known brothers and sisters who were friendly and nice to each other, but the bond I saw between the Bride and her brother was different. I thought, some day I want that for my children too.
I have two sisters, three girls growing up in a tiny house with different interests and aptitudes. When we were young, we played together. I remember our electric Hot Wheels track, Barbies, Operation, UNO, Go Fish, Mad Libs and backyard softball. I'm not sure when things changed. I remember fighting, feeling bossed around and very lonely.
Fast forward 30 years. I have seen numerous sets of siblings show me what it really means to be family. My friend who's oldest sister moved her other sister, brother-in-law and two teenagers in with her when her sister was diagnosed with a devastating neurological condition; the twice widowed stroke survivor who lived independently because her sister and brother-in-law lived next door; the 98 year old sister feeding and pushing her 104 year old brother around in the nursing home and the construction worker brother transforming into nurse, secretary, bank and chauffeur for his brother battling cancer.
I have had several conversations with my mother why my sisters don't help each other (or me) like our cousins? I want to be positive and believe that things can still change, but above all else, I will do whatever I can do so that my children love and support each other until the day we all meet up in Heaven.