I am so sorry for the loss of your precious parents. That is something that you learn to live with, but it ALWAYS affects the rest of your life.
Finn is to be commended for keeping you all together, and I hope that everything goes well with all of you. Your brother, understandably, has a lot of anger.
It is normal to be angry at your loved one when he/she dies; it is part of the normal cycle of grief. Finn may also be angry because he has the responsibility of raising the rest of you...on top of that, he probably feels guilty because he has anger issues. It can be a vicious cycle to break free of...
I have lost people I loved, way too soon, and it hurts. It can be normal to feel mad at the world, mad at God. My belief is that God is loving, and doesn't "take" good people to anger the ones who remain, but he "accepts" them, welcoming them into Heaven.
Your mom fought hard to survive Leukemia, but lost her fight. It was not because she didn't fight hard enough; it was because God was ready to receive her. I really do try to look at death that way, even though the loss of a loved one is hard.
I am a hospice volunteer, and am often around patients who are terminal. Helping them (and their loved ones) deal with the end-of-life issues is hard but rewarding.
Perhaps you can convince Finn that because religion was important to your mom, you want to explore it. I admire you for wanting to follow in her footsteps; I am sure she would be proud and relieved. I also believe that she is watching over you as well.
If Finn won't let you go to church, he can only stop you until you are 18...and you can take religion classes in college, or possibly in school as an elective soon.
Also, you have the Internet, which can provide you with a lot of knowledge. Do you have, or can you get a Bible? If not, email me; I will send you one.
The stories of the Bible are so important to know, and it is one of the most entertaining, heart-breaking, exciting, thrilling book syou will ever read.
Spirituality can be a very important, centering part of your existance. You do owe it to yourself to explore, even if you have to wait until you are an adult.
Good luck to you; you may email me if you would like to ask questions or have me send you a Bible. I am a mom, a Sunday school teacher and a youth group leader as well. I get kids, and God. It's a wonderful combination!