How should I ease my intense hatred towards my mortal enemies?

I think you really need to take a deep breath and let it go. Your making yourself sick with hate over something you have no control over. No one can control another person. The only one you can control is yourself. Maybe the kids didn't know the aunt that well so they didn't feel anything when she passed. Maybe this aunt really is in severe pain and can't walk. You don't know for sure. All that really matters here is that you cared about her. The rest doesn't matter in the grand scheme of things. In 100 years you'll all be dead and no one will remember any of this.

Why do you not just accept that your aunt might be a selfish person? There may be a myriad of reasons why she did not attend; these may vary from an age-old argument, which you don't know about, to the current excuse that she had a bad knee. Whatever the reason, you don't need to hate her and her kids! Tolerance and Understanding are great assets, and if you think about it, your attitude could benefit from some serious thought. The children might always have been disassociated with your aunt.

Accept the family differences and move on. All families have problems of some kind and if you are an idealist, it will grate.

Sometimes, family doesn't step up to the plate. It sucks, but it's true. As much as it seems to infuriate you, you have to realize that the only one effected by your hatred is yourself. All that time and effort you are putting into building up those feelings against them is a complete waste. It won't end in anything positive for yourself. Your Aunt, she made a bad decision, but in times of grief bad decisions are always made. She'll have to suffer the consequences of missing out on a chance to see her sister by herself. Having such negative feelings towards her is causing you to suffer right along side her. Don't think about That's the best advice I have and I honestly hope it helps you. I'm sorry for your loss.