Death is a bomb. Grief is the shockwave. So the closer you were to the impact (person), the more you feel it. In the case of someone you love, you were right there next to it. The effects are thus felt much stronger, & may last longer, but at the end of the day: the bomb did not hit you. Even if it feels like it sometimes. Only the shockwave. You are alive, and we the living must carry on, for ourselves & also in loving memory of our dead.
That doesn’t mean bottle it up and ‘move on’ or anything like that. In fact, closer to the opposite: Feel it, and give yourself time to feel it. Be patient, be compassionate, with yourself, & with others. Don’t judge yourself or others too harshly for a while if things get crazy; it’s inevitable at times like these, & it’s ok. And, it shall pass.
Two things jump out at me immediately, upon reading your specific story:
1. Between the wife whom you describe as amazing, and two twins on the way, it sounds like you have a great support system, as well as plenty to live for. Those are both incredible blessings, to be in love and to be a father; so hold them dear, and do not take them for granted as you go through this aftermath of tragedy. As you know, many who go through the suffering process of grieving are alone, they do not have those things in their life to back them up, or to live for. Your wife, your kids, they are the garden that grows, long after this storm of grief has passed. Keeping that perspective will help you as you go through your own grieving.
2. Your father sounds like another great thing, so lean on him for support as well; but also, make sure that particular street goes both ways: Be there for your father. (Assuming he is also your brother’s father.) There is perhaps no greater tragedy a person can suffer than to bury a son or daughter. Same for your brother’s other loved ones, be there for them in this time. Not only will you help them, but I have found that a great reliever of one’s own grief, is to help others survive & get through theirs. We’re all in this together after all.
RIP to your brother. And deepest condolence from me to you in this hard time.