when I look at my touring stuff weights, the tent is a big item, so having a very light Tarptent will help a lot in the total weight. Its fairly easy to smartly choose layers and whatnot for minimal clothing, but this will totally depend on when you go, where you are, what temps are in the works, and how much you are willing to be uncomfortable / put up with cold etc.
The food and water, especially water, is the real kicker for weight here. I liter of water=1kg, 2.2 lbs for its pretty darn easy to get heavier fast, and food too.
Another big recommendation for a filter, you may not think its an issue, but filtering water is a pretty basic precaution against Giardia etc, which aint fun. Filters have a wide range of prices and weights, but the sawyer ones are pretty light, although you can't let them freeze---but this is a whole big topic for you to look into (filters I mean).
re tools and stuff, I'd highly recommend that you ride your bikes a lot before the trip, and get the spoke tensions checked out well before the trip too, just to eliminate technical stuff --basically make sure the bikes are in great shape but ride them a reasonable amount after any work, to be sure all is good.
if you want to get all detailed about weight, go ahead and start listing what you think you'll be bringing, get a kitchen scale, and weigh all your stuff individually and start tallying up total weight, and especially seeing the actual volume it takes up. Thats the one thing that is tricky without panniers is the room for extra food and water.
good luck planning and figuring what stuff and how it will actually fit in and on your bike. Not having enough water sucks big time, so to me this will be the main issue.