They will definitely fit the rims. Measure the space between the top of the existing tire and the brake bridge, and the space between the side of the existing tire and the seat- and chain-stays or fork legs. If you have at least 5mm to spare under the brake bridge and at least 3 mm to spare between the tire and stays or fork legs then a 28 mm tire might fit. If it seems like it might be a tight fit, assume it won't work and make sure you can return any tire you get if it doesn't fit.

The other optrion would be to go to 25 mm tires... not as big a differnce, but it might help.