Just my opinion... Please don't give him a "diet package." You may think you're close as brother and sister, but even if my actual siblings had given me such a gift when I was obese, it would have broken my heart, and it definitely would have cooled my relationship with the giver.
If you want to give him a diet book, do it out of the blue--and don't make a big deal out of it. Just take it to him and say, "I thought you might like reading this because I found it helpful." But for Christmas... well, I just think it's not a good thing to do.
Here's a thread on a diet book discussion that we had here in Support a little while ago:
http://www.3fatchicks.com/forum/showthread.php?t=125493
Also, you can read reviews of lots of diet books starting from the 3FC main page!
Jay