Wendy-
You are correct that usually Ren/Fielding have you meet with the nutritionist first, then come back to meet with them. However, in my experience, once I met with Dr. Ren, she offered me a surgery date 2 weeks out, which was too quick for me, as I was travelling on business and could not do the 2 week liquid diet at that time. You may be able to get in quicker than you think.
By the way, all three of them are superb physicians, so you are fine with any of them doing your surgery. Good luck!