Dee, please accept my deepest condolensces on the loss of your father. I know how tough this is and how devasting it can be to a family.
First, the ex. Of course, the proper ettiquette would be for your ex to acknowledge your father's death. But, your anger at him isn't constructive for you. You are angry at him because he is the easy target right now. You need to forget about your ex. This is about you and your family and how to cope with this huge gaping hole in your lives.
Your Mother's reactions are quite normal. Everyone deals with death and grieving differently. Your father was her spouse. She lived with him day in and day out. It will take her longer to work her way through this. I know you are worried about her. That is good. Be there for her when she reaches out to you to tell you she needs you to be there. But please know that the days she gets out of bed and does the things she has always done is a very good sign. There are some people who do not get out of bed at all. Just accept that some days are going to be better than others for her, for a long while to come. They were married many, many years. It is so very difficult to adjust to being alone. You have to let her grieve in her own way and in her own time. Just be there for her and give her as much encouragement as you can. Make her smile. Make her laugh. Take her out to dinner and a movie. Take her shopping or to a museum. If she doesn't want to go, don't push. Just let her know that you are willing when she is up for it. If she has good friends, you may want to call them and ask them to check on her and invite her out to do the things they have always done. Again, they shouldn't push her but make sure they don't forget about her.
As for your brother, he is coping with this the only way he knows how. You will both eventually be able to find common ground and find a way to talk about the positives regarding your Dad. You will share the good memories. Trust me on this, it will happen. Right now, it is still too early. When he needs you, he will call. In the meantime, you can also just call him and check up on him. You didn't mention if he has a family. If he doesn't, invite him out to dinner or over to your place for a home cooked meal. Again, don't push. Just let him know the invitation is there. He will reach out to you when he is ready.
When we have never experienced the loss of a close family member, we find ourselves in a state of shock. It is a whole new experience of emotional turmoil we have to figure out how to constructively deal with. You are right in that you do find out who your friends really are when someone we love passes away.
I can see from your post that you are in a state of flux right now. You feel unsure of how to handle everything and you are worrying and thinking about everyone else. You need someone for you to share your grief with, and your Mother and brother aren't available. I think it might be very beneficial to seek out the help of a Grief Counselor or join a Bereavement support group. A professional can help you get your thoughts sorted out and allow you to express your emotions when others won't. It might also be a good way to figure out what you can do to help your mother and your brother through this. You can express your specific concerns about how they are coping, and you will receive constructive advice on those problems. A support group is a good way to find others who are going through what you are going through. You can help each other heal and find create new friendships in the process.
I don't know where you live but these links might be of help to you.
Grief Counseling and Grief Recovery Resources Chicago, Illinois, USA
GriefShare: Grief Recovery Support Groups
You also might want to go to your local library or bookstore and search for books on Bereavement. There are a number of good ones out there for adult children who have lost a parent.
If you have any questions or specific concerns, you can always post back here. We will help you as much as we can.