Brother, 52, has been told he has obstructive cholelithiasis. does this indicate gallstones in the common bile duct instead of the gallbladder?

Stone in gallbladder does not cause obstruction. When a stone moves out of the gallbladder, coming down along with the bile and the stone is stuck on his way to the intestine then the condition is called obstructive cholelithiasis. The term cholelithiasis means stone(s) at anywhere in the biliary system. However, when stone(s) is (are) seen in the gallbladder, we call it (them) gallstone(s).

This means a gall stone stone obstructing the gall bladder.