I read carefully all you concerns and I am so sorry for your father situation.
IF i were his treating doctor I would recommend take exams like:
-Ct- scan ( abdomen)
-Gastric Passage( contast exam of small bowels)
I am hapy tha upper endoscopy
are normal, but he need to be evaluated small bowels. It Is possible that the site of hemorrhage is in small bowels.
Wish him health