My kids all slept in my bedroom until they were about a year old...I didn't consider it a "bad habit," but rather something that helped me to get more restful sleep. I didn't go into parenting expecting to co-sleep...its just what worked best.
I'd encourage you to gently transition your son if this sleeping arrangement isn't working for you--especially because I'll assume he was born a bit premature, so you really can't consider him to be the same maturity as would usually be referred to as 11 weeks old in most "sleep training" type books.
So to gently transition him...if you have a pack&play with a bassinet insert, that will be VERY helpful. Put it next to your bed. Fold up the fitted sheet and stuff it inside your shirt to wear around for a few hours so that it gets your scent. Then put it onto the bed just before you put your son down to sleep. Put him to sleep in the way you normally do, and then once he is totally out (limp like a dish cloth), gently lay him into the pack&play.
Work with that for a couple of weeks until he doesn't seem to be needing you as many times at night, then I'd encourage you to transition him to sleep with his twin--my first child was the hardest to transition out of co-sleeping because moving from co-sleeping to sleeping all alone was too huge. She really didn't transition until her younger sister was 6 months old, and we put them together.
Good luck!