Dear Eva,
Children are cruel and heartless like that. Of my Step Children, one is distant and uncaring, one is the nastiest, most selfish person to her Mother and myself, the third is sweet and caring. They were all brought up the same by both of us. Ignore the spite, they need you more than you need them - try turning your back on one of them once when they come, pleading.
As to your brain being 35, mine is 23 in some things. I crave humour, have it on all the time. It doesn't make me happy, just takes the edge off the darkness. Comedy is a pleasant noise to block out thoughts. Live in your younger brain.
Always remember, whatever happens there, you are loved and appreciated here.

Dave.