I would also have you younger children tested. IBS is a symptom and not a cause, the cause could be celiac. ADHD is often food linked too. What's Eating Your Child is a great book that discusses how diet affects behaviour; you might want to take a look at it.
My three boys all tested negative for celiac but like your daughters, they had varying degrees of gluten intolerance symptoms. We decided to make them gluten-free along with me because eating gluten-free can't hurt (as long as you don't replace wheat with sugar laden gluten-free substitutes at every meal), it could help them feel better, plus it was easier if everyone ate gluten-free in the house from a food prep point of view.
Even though my boys had negative tests, two of them have shown real health and behaviour improvements on the gluten-free diet. My oldest is putting on a bit of weight and growing, has less headaches and stomach aches, and his mood and concentration has really improved. My youngest used to have to visit the bathroom for bm's 5 to 8 times a day and now he's down to 1-3 and has grown a LOT.
I mention all of that to encourage you to try the gluten-free (and possible dairy-free) diet for a few months once your daughters' testing is done regardless of the outcome. Non-celiac Gluten Intolerance is much more common that celac is, and could be causing their health problems.
Thank you! That's what I think is going to happen....waiting to talk to regular pediatrician tomorrow