Please see this article:  

Exciting news for sure, especially the fact that "existing drugs could be used to interrupt the inflammation process and help treat patients." Having to develop new drugs to target this genetic pathway would take many years, so finding existing drugs that do so could greatly speed up treatments.

Since your daughter has celiac disease some studies show that up to 44% of first degree relatives also have it, and it sounds like it is very likely that your house may be going gluten-free soon, mostly anyway, due to your daughter's recent diagnosis. If you are in the UK (since you spell it "coeliac"), you may get subsidies and other health system benefits if your son is also formally diagnosed, however, the situation you describe would be very difficult to deal with, so I would have him go gluten-free ASAP to see if it helps with his symptoms (but be sure to alert his doctor that you are doing this, and why you are doing it). If his test is positive and his symptoms improve on a gluten-free diet, try to get the doctor to diagnose him without a biopsy, otherwise he would need to eat lots of gluten each day for 2 weeks before doing a biopsy. I hope things improve for him, and let us know how the test results turn out.

I've not been to Australia, but they have one of the strictest gluten-free standards in the world, and I've heard that going to the larger cities there is easy for those who are gluten-free.

There is plenty of gluten food that is unplatable also. The trouble in restaurants is that wheat,  like the Frank's Hot Sauce commercial; "They throw that bleep on everything." In my opinion, the underlying problem is compromised immune system due to vitamin D deficiency and Green Revolution modern wheat.  50% of the industrialized world are vitamin D deficient and we are urged to avoid sun and limit oral vitamin D intake to the minimum.   Non Celiac Gluten Sensitivity became an official diagnosis only 10 years after modern wheat was marketed.