My Mom and I went to Europe recently for 16 days and it was hard leaving all three, so I understand what you are facing.
We left them with my Dad, so it's someone they live with anyway, so of course that made it easier.
I'm sure you trust your brother though and I would make sure to leave written instructions on her schedule, so she can stick with her same routine!
Just tell your brother to give her special attention & love!
