Hi...
I would suggest removing cows milk and cheese from their diet as soon as possible. There are several subsitutes for milk on the market now. You could also ask your doctor about giving them MiroLax (1/2 the recommended amt for adults) every other day at night in their water. Its clear (once dissolved), tastless and can be mixed in juice or water, even soup!!
Process of elimination...try the milk and milk products first and see if that makes any difference.
Good luck with those lil' beauties!!
DEFINENTLY take them to a GI Dr. Or try a Children's Hospital, where they have specialists who can figure this out! Poor babies! I'm so sorry. I have the same problem, and was just diagnosed with gastro problem's and Lymphangiectasia.....I have been introduced to Aloe-vera juice, Diatomaceous Earth, and most importantly "Body Ecology"...please give this a try! I am getting some relief after being sick for a long time! GOOD LUCK
Welcome to the gastroenterology community! Have they seen a GI doctor about this? Have they had any testing done? This is concerning, especially because there is blood, and they really need to have testing done.