One small thought
Sifra, the Tannaitic midrash ad loc, asks why such enumeration was necessary. If the Bible had said only siblings, we could have learnt logically that children are also included in this category. Why? Because a parent has legal obligations toward his children - their education, their welfare are the legal responsibility of the parents. But siblings do not have formal obligations towards each other.
But, I'm thinking, now that siblings are included in the category of people for whose burial a Kohen is required to defile himself, what does that tell us? Doesn't it mean that the relationship between siblings really is one which carries mutual responsibilities? In life, and in death.
I wanted to post something tonight in memory of my grandmother's first cousin, Eliyahu Hershkowitz, who was one of the 35 Palmah soldiers who set off in January 1948 to relieve the siege on Gush Etzion. They were all killed before they reached the Bloc.
So, one of my responsibilities to Eliyahu, who was an only child, is remembering, telling his story. Another is serving in the army that he would have joined, had he lived a few months longer [the issue of Israeli citizens who consider themselves exempt of any duty to enter the compulsary draft is an incendiary one I don't want to enter into, but, especially on Memorial Day, it seems like an incredibly selfish, callous position to take, that Haredim do not serve]. There are more responsibilities, of course. And other siblings to whom I owe them. But that's enough for tonight.