You could use the general formulas for angle between vectors found here: angle-between-two-vectors-in-3d, which is a good answer. If you desperately need the angles relative to the points 2 and 3 pair you will have to do some elementary linear algebra and rotate your coordinate system such that the x-axis lines up with the direction between them. From there you should be able to figure out how to use atan2 to get the angles you request. As usual it is very helpful to sketch the graphics of the steps on paper to get a clear image of what's done.
HTH
