Thanks for your query.
Of course he is prone to develop sore bum by repeated wiping.
Sticky poop which is difficult to flush reminds me of a term called steatorrhea
(excess of fat in stools)
Such stools are often seen in Malabsorption
(failure to fully absorb nutrients from the gut) and there are many causes including abnormalities of the gut wall, failure to produce digestive enzymes and abnormalities of gut flora
Please get his stools tested for the same.
Hope you find the information useful.