[pushkins]

If the boards are glued to the beams then the squeaking should be very minimal if at all.
What your husband may be seeing is movement at a joint between two sheets, right in between the floor joists, this can be helped by simply cutting a piece of wood that matches the size of the existing floor joists (2"x10" for example), applying glue to the upper surface and fitting it in between the floor joist under the joint and then attaching it to the existing floor joists on either side by nails (from the other side) or screws.

Your bathroom may be a whole different beast to fix, without removing drywall from below the only way to help fix the squeaks is from above and that usually means dealing with tiles.
The bedrooms are a little easier, but it will envolve the pulling back of the carpet and using screws to fasten down the sub floor to the floor joists, the best screws to use are exterior 1 5/8" (they wont snap off) follow the nails in the sub floor and put screws in every 10" - 12" then simply have the carpet reinstalled (should cost all that much).

In many cases builders use nails to hold down a sub floor because it is quicker (with a nail gun) some nails will over time work their way loose and there ya go....squeaks !!