One way that I've used recently is to have one NAMED_HIDDEN_ANS and to use a list answer checker. On the Javascript side, I use JSXGraphs's on method to provide a callback function for whenever a point is moved. This method writes the points' coordinates to the hidden answer field as if a student is entering a list of points (so each point surrounded by parentheses, and each point separated by a comma). You can then (in Point context) just do a list answer checker.
HTH,
Steve