There appears to be two conditions that your dad has. It is unfortunate that he was not diagnosed with Celiac disease sooner as it can be well managed with avoiding foods high on gluten. Among many other complications that you may already know, this disease can have severe malabsorption leading to osteoporosis, tooth enamel defects, central and peripheral nervous system disease, pancreatic disease (i.e. pancreatitis, and internal hemorrhage). In your father's case of longterm exposure to gluten, the small intestine of a patient with celiac disease can become atrophic, losing their surface volume and compromising their absorptive capability. I am not sure how this affects the stomach but he certainly would benefit from a complete GI work up. It is, however, not clear how stomach ulcers are linked to small intestine atrophy. Intestinal rehab program focusing on optimizing enteral nutritional support
several issues here may not at all related: stomach ulcer
and small intestine absorptive ability.
If all fails, an intestine transplant is needed. It is best to discuss this issue over with your internist
to come up with a strategy to treat your father's stomach ulcers and small intestine atrophy. Your father would benefit from seeking help from a gastroenterologist
(GI and internist). Good luck.