A mix of moods that put them over rational thinking
Maybe they feel as if life isn't good enough for any of them, including their-self.
cuz when you're THAT BAD-off, you cant see that. depression has a strange way of making you see things all fuked up- you're interpretation of everything becomes skewed- its a mental illness!
I have no idea
Some do it because they think they'll be reunited in the afterlife. That's what I've read. Others might do it so the family won't have to suffer from their suicide, or as revenge that they can get away with if they really don't like their family.