hmm,, so you need the real position of your objects right?
if you want to do that you must calculate all elements of matrix transformation for all node above your testNode ( not only translation but you must consider every transformation include scale and rotation)
here's my code to calculate real position of a object, and the parameter of the function is your testNodeTranslation point
groundNodeTransformation is your Transformation of your gound node and markerNodeTransformation is Matrix Tranformation of your marker node
public static Vector3 ConvertToRealPosition(Vector3 pos)
Matrix trans = groundNodeTransformation * markerNodeTransformation;
return Vector3.Transform(pos, trans);