I'm not Dr. Doug, but I did make note of the "dosage" he's given for fish oil in the past, which is 22 to 40 mg. per kilogram of body weight per day. A 10 pound dog is about 4.5 kilograms, so that would be about 99 to 180 mg. per day.
Note that is for the combined amount of EPA and DHA, which should be listed on the label. It's not the same thing as the total milligrams in the capsule.
What I would do is use a pin to poke a hole in the capsule and squirt the contents over both dogs' food every other day. Splitting the contents of one capsule should give them roughly the same amount they're used to getting.