Shelly
The 40D is fine and I'd have the 18-50 f2.8 on that. On the 400D, the 70-200 f2.8. THe 400 is a fine camera but is not as well suited to wedding photography just because it's not the quickest camera to work with. When under pressure you need to know your equipment inside out and be able to change settings quickly.
Rather than use the 400D as a backup, make use of it during the day to capture the story around you. If either fails they backup each other.
The 28-135mm IS is a slow lens. When shooting in a dark hurch you woill struggle to get decent shutter speeds and you will almost always be at a very high ISO.
The Sigma 18-50mm f2.8 is a nice fast lens. Not as good as the canon 17-55 f2.8IS but decent nevertheless.
The Sigma 10-22mm is another excellent lens and use of the perspective can add a fdifferent dimension to your wedding. I use my 10-22 sparingly though.
Canon 75-300mm - You have the 70-200 f2.8.... I'd sell the canon.
The 70-200mm f2.8 is a fine lens - again not as good as the canon but still a cracking lens. Only problem is you need to maintain a shutter speed above 1/200th to get sharp images.
THat's why I went with the Canon 2.8L IS. Shooting at 200mm 1/30th sec with IS is just amazing!
I agree with Kryprix - buy a couple of primes for low light situations. A 50 f1.4 (no need to go for the L) or an 85 f1.8 (again no need for the L) are excellent. The lenses do make life easier though
I carry my two cameras with the 70-200 and a pick from my other lenses depending on the wedding and conditions. THe 70-200 is glued to my 20D - it's that good!
What about flash? You need a couple of these too. 580s are the standard flash for a wedding