a. Use the Symbol font. It has several parts of curly and straight braces and parentheses, designed to stack upon eachother with zero extra leading (or slightly less, if you want a smaller brace).
b. Put these into an Anchored object, anchored somewhere at an appropriate place, so its frame will always keep the same relative position to its text.
c. Well, it oughta look like this. On the left: a frame with three parts of a curly brace. In the middle: some random math. The top line “contains” the anchored object, as can be seen by the ¥ sign. On the right, the anchored object itself, positioned relatively to its anchor.