It's normal for fibre to give you cramping, bloating, gas, this is normal and even happens to healthy people, once your system adjusts (took mine 3 months) it's well worth it, you know what they say, no pain, no gain...I'm talking fibre supplements recommended by my GI (who happens to be in the city and I live in the country and we only have one hosptial with only one GI who sees people on an emergency basis only, not regular patients like in the city...another "hard to believe" but true).
Always start with a small amount of fibre and slowly increase if necessary and drink plenty of water with it.
Maybe you should see your GI's brother if he's telling you that about fibre, fibre is infact digested by the body, fruits and veggies are fibre and are more easily digested than the processed garbage out there that people are filling up on. Infact, avoiding fibre is about the worst thing anyone (unless you have crohn's and issues with strictures, but even then, low fibre is still necessary) can do is avoid fibre all together.
Fibre helps with either C or D, helps sweep the bowels clean of bacteria, helps keep the bowels functioning properly and IBDers need all the help they can get with that.
Fistulas are mainly related to crohn's disease not UC, you'd find out if you have one by having your doctor (or his brother instead maybe) take a look.
If you have inflammation in your rectom, you need rectal meds for sure... DO NOT QUIT PREDNISONE cold turkey, or your adrenal glands will go all whacky on you, it's not a safe thing to ever do when taking prednisone.
Honestly, this is your health...if you are not comfortable with your current GI then by all means you have the right (without feeling uncomfortable) about switching (brother or not), besides the fact that maybe the other GI isn't as good as the one you're currently seeing, if that turns out to be the case then head to the nearest city for a new GI, it's a pain in the ass of course, but so is having IBD so you'll get used to alot of pain in the asses.
My bum is broken....there's a big crack down the middle of it! LOL :)