Hi everyone - I'm new to these forums, and have been gone a long while from backpacking, but looking forward to get back into the groove.

I have a somewhat unique situation that I'm looking for ideas on. I still need to get a pack, and I think I'm going to make a Ray-Way 2 person quilt (thx to the advice of someone here). My unique situation is that I want to be hiking with my almost-7-year-old son, and my wife. My wife has MS, which puts some restrictions on how much she can do. Basically, MS has stricken my wife in a way that limits how much she can exert herself before she starts to get debilitating symptoms. But we're dedicated to not letting that keep us indoors, and more importantly, keeping our son away from the TV.

So my attraction to lightweight backpacking isn't just the usual benefits, it's kind of a necessity. It's already a given that I'm going to have to carry the bulk of the load for the three of us. I think I can comfortably handle about 40lbs, and my wife and son could each handle roughly 10 to 15lbs. I'd like to try 3 to 4 day trips. I'm thinking that I structure the loads this way:
Me: main pack (I'll have to get internal frame I think - suggestions on volume?), with quilt for my wife and I, tent (6.5 lb Kelty), my clothes, stove and fuel, UV water purifier, cookware, and half of food.
Son: his bag and pad, his clothes
Wife: our pads, other half of food, first aid, and toiletries.

Can this be done? Do you have experience and/or suggestions to make sure this is successful? The most ideal situation would be that my son and I carry everything... I know a certain amount of this is going to be trial and error, but I'm looking for the expert minds here to flatten the learning curve as much as possible.

Thanks!