It sounds like you and your brother have different communication styles and Love Languages. I won't touch on love language in this answer but it is very interesting and may be helpful for you to look into.
Based on how you described the situations, it might be helpful to have a sit down discussion with your brother, one-on-one not your whole family, to talk about how you see the situation, and how he sees the situation. But if you choose to talk to him, to be the most effective and least threatening/accusatory, this needs to be done in a neutral place and at a time when you haven't just been asked to do something with him or asked for him to do something with you (which seems to be the behaviours that are the issue). This may only be effective if you are both willing to talk about it and learn from the other how your actions and words affect one another.
I also find that it can be helpful not to try to come up with a solution to the problem in the first initial conversation. We can learn a lot about ourselves and others by 'sitting with it,' meaning talk about how you are feeling and what you are both thinking and then think about it passively over the next 24 hours or so. This can help you to notice any emotions that you may not have noticed in the moment, and check them before you try to solve the problem.
I always give him a few days heads up when I would like us to hangout or I need help. My schedule is super busy so I treat everyone else's the same. Therefore he can arrange his plans accordingly if he chooses to help.
This is a great solution to your side of the problem. Often we don't notice that other people are doing things for our benefit. My suggestion would be for you to include explicitly explaining what it is that you are doing, how you see that it benefits both of you, and listen to how he interperts the same situation. for example:
I try to give you a heads up when I want to hang out with you, it helps me because I am really busy and I can schedule my time better, and I know that you are busy and I want to be able to let you schedule your time as well. It makes it so that I can spend real quality time with you, which is something that I really enjoy. And then pause and see what he says. He may be surprised that you are doing this, based on what you described you are very busy and he may just think that you are asking him well in advance for your own gains and not for his benefit at all. You may find that it is actually a nuisance for him to schedule his time 3 days in advance.
Keeping an open mind and allowing for compromise on both sides of the situation is extremely important. Look at the situation from his perspective as well and try to come up with a solution that works for both of you. Keep in mind that the solution your family has come up with: 'How can we talk to him so that he will agree to give us more notice' may not be the solution you land on.
Humans are very complicated emotional beings and being open and honest in our communications can help to elevate the confusion.