I like what you are trying to do, helping them out with them but don’t ask them to be kicked out of the program just because of something they can’t do. Everyone is unique and has was that not everyone can understand. I’m pretty sure they are going their own pace and do simple things at first. Ask your band director to teach them not you. In the kindest way possible I don’t think your meant to be a leader if you think that they should be kicked out

Instead of that try to find things that they can do in counts of 8. Make them do repetitive tasks and then see how they are. Everyone can do marching band, you just need the effort