Like SD said, spouses together can be counterproductive. It very much depends on whether the two of you can both be absolutely certain that having the other one around won't change your behavior--which is pretty much the norm.
You might be able to take one weekend class (beginning to sail) alone while your wife has the kids, then swap while she's off. Get the basics under your belts and compare notes, because each of you will have a slightly different experience and that's a good thing. Then, once you've gotten the basics of sailing, do the bareboat thing together, because managing a boat with systems on it is totally different from the sailing part.
In terms of rates...I think that if you told any sailing school you both wanted to do it, but wanted to do it separately, they would understand immediately and still give you a "couples" rate.
If you're one of the rare couples who only reinforce each other...it might be great, but this is "lessons" not a "vacation", think that over carefully.