I had a "living with my parents" stage, though it was before I got married. My dad told me one time, "you are in MY house and you need to show respect and follow MY rules."
I kind of imagine that the living room is the only room your parents feel is safe (child proofed or whatever). If you are watching 2 other children during the day, I infer that they have to follow the same rule. And do you offer this "watching" service with a fee? Please don't be doing it for free!
A baby monitor might do the trick of allowing your child to "call you" when you are in another room. You might get one donated to you or find something similar that is low in cost.
I don't necessarily find it bothersome that your parents insist that your son stay in the living room; but I do when they say he can't be near you when you are out of the living room. My youngest son got the ability to get out of my sight in the blink of an eye or "quick as lightning," so I would understand keeping children from wandering around unattended (the attempt to clean Sharpie marker off of a wall was NOT fun or worked very well).
Maybe you can come to some sort of peace with your situation given all of the responses you have received. I also know many mothers who believe in "Attachment Parenting" that they would be appalled that your baby is kept away from you. He can only cry to get back to you, since he can't call your name yet. Answering that cry quickly is one of the foundation principles of Attachment Parenting. You give your son the comfort that he is not alone, that he is loved and that he is special to you. A care-giver can do this, but not nearly as well as the actual Mom.
Check out the cool book review at http://www.llli.org/NB/NBJulAug02p142a.html