I agree with everyone else. Here are my impressions:
1) I feel there's still too much tension in the beginning. (And I also use a strong person on the ground, when need be---keep your good brother around for awhile.
2) After you get halfway on, get off. Personally, I'd then give a treat. Plenty will disagree with me, but I feel if my horse will eagerly take a carrot bit or cookie, all is well for all of us. When she is not interested, there's something wrong---there's too much tension, and I take that as a serious warning. Then half-mount from the other side. Until it's really a non-event for your horse.
3) I don't know how much groundwork you did before the video, but my approach with a young horse is to let him know EXACTLY what is expected. I would either lunge her in a small circle, or have your brother lead her. Then upon mounting, no standing around---this can build tension too-- just do the EXACT same walking in the circle. Then get off, and do the same thing the other way. Treats, of course...
Anyway, that's the way I'd start a nervous horse. Please be very careful. The motto at my house is Safety First. We always allow ourselves to "back down" or what seems backwards in progress. Right now I feel getting your horse to be much more relaxed and complacent, more confident that he knows what the story is, is the priority.