Get the colonoscopy. I waited too long for my son. It was already pancolitis and in 3 months time, his colon was out. I feel for you. It is so stressful to worry about our children having this disease. Both my husband and son have jpouches. Been through just about everything, so I consider myself an expert of sorts although I wish I didn't have to be.
My husband has a very successful j pouch for 13+ years now. UC runs rampant throughout his family. His niece (my son's 1st cousin) has a permanent ostomy. My hushand's sister died of colon cancer. His father had UC as well as 2 uncles and another cousin with Crohns. My Son's 1st jpouch failed and he had a redo last October. He's still struggling with complications.