Ordinarily I don't like to suggest that mamas cut dairy from their diets. Most babies outgrow their allergies/intolerances and I don't personally think that there's any data suggesting that dietary restrictions on mom's part do much to help the babies in the long term. Especially since you don't KNOW what a baby is reacting to- the major offenders are cow's milk, wheat, and soy, but a particular infant could be reacting to a less common allergen.
That all being said, at this point I think it makes sense to try a diary elimination. See if anything changes. There's lots of information on the forum about how to go about elimination diets, how long to give it, where to find so-called "hidden" dairy.
Hang in there, mama! I know this is super-frustrating. But please focus on the positive- you are feeding twins on 100% breastmilk! And they're gaining weight nicely. It's a huge achievement!