Can my brother attend the AGM as my proxy?

This is a fairly straightforward answer - 'yes', you absolutely can nominate your brother as your proxy, to attend and vote for you, and to be on the committee for you. The prescribed statutory proxy form has all of the options clearly laid out on it, and your manager will include a copy as part of the AGM notice.

Three important points to remember:

1. It's best to be explicit on the degree you are empowering a proxy. If you mean for them to represent you on all matters, note that on the appropriate section of the form 'authorised to speak and vote on all matters', OR, if you have specific instructions for a particular item, add that in, '...other than item 17, the fence replacement, to which I vote in favour of quote XYZ'.
2. Appointing a proxy doesn't change the need for you to remain financial at all times. If your financial status changes, your proxy can no longer vote and/or will be suspended from the committee, just as you would be.
3. Specify the date of your proxy having effect, noting it has a maximum of 12 months. You may need to update it before the next AGM. Maintaining the authorisation is important and should be the lot owner's responsibility, rather than the manager's or committee's.