Hi Ashley, Welcome to healing well forum, we are happy to have you join us here. It sounds like you have so very much going on in your life and your family. You didnt mention your dad...does he live with you and is he any support for you? I dont think your being selfish persay, but when your little sister is born really cant be helped. Yes, it may take some attention away from you around that time frame as babies take alot of time and attention but, hopefully your parents will step up and make your sweet 16th birthday as special as it should be.
As for your brother, I wonder if you have spoken to him and let him know how much his actions and behavior has effected you? Usually, people become addicted to drugs and other substances to hide from the realities of life. He is so young to have so many problems...are your parents aware of what is going on with him and if so have they done anything to try to get him some help?
I am so sorry about your grandmother. It is difficult to deal with the reality of knowing that someone you love has a termal illness like that. You do have time to spend with her and that is priceless, use that time well and cherish it.
Please know that you can post here anytime, we are always here.