Everyone has their own timing when it comes to healing. I think they should understand that you are grieving still. If you need to talk about it, speak about it with some who won't judge and are all ears. Talking does help as I grieved for my father who died when I was 15. Take your time with healing.
I had that question too and as others said It depends on you. But I read some self help book that an average is one month per year of time spent with that person. That satiated my curiosity for an answer, so I hope it helps.
I don't really have any experience with what you're going through, and I apologize if my response doesn't fully address what you're feeling. But I think grief is something personal and extremely variable. You shouldn't be made to feel guilty or wrong for being sad. However, if you think it's getting to be too much, or destructive to your own mental health, you could try finding professional help, or at least a supportive friend to talk to.Also, keep in mind moving on isn't something you do all at once. You likely have already come a long way. Every time you take an interest in a topic, discover new music, have positive interactions with friends, get involved with a cause, or anything that contributes happiness or meaning to your life, you are in the process of moving on. It isn't necessarily a decision to not be sad, but a continuous effort to participate and grow anyways.
I personally dont think you necessarily have to every "get over it" so long as your living a healthy life. I know that sounds really contradictory but he was your brother who i assume you where close to, that is something your never going to forget or be able to just one day wake up and not feel sad about it. but, i do believe that in your time, you wont feel so sad all the time. I assure you you will think about him every day and feel sad but dont let that overwhelm your life.