Patrick,
While the Weyhill course does not share the same clubhouse as the Old and Grace courses, several holes border the Grace course. All 3 courses look like a contiguous 54 holes from above (actually 60 holes, with the 6 practice holes). And I do have proof to back it up if you'd like.
The Cliffs in SC, mentioned earlier, is a great example, as it has 3 courses, all separate. Glassy and Valley are a few miles apart, at the top and bottom of the same mountain, and Keowee Vineyards is probably 30 miles away via winding roads.
I believe sister courses Devil's Pulpit and Devil's Paintbrush in Ontario are not neighbors, though I'm not sure if they're considered "the same club".