I want to animate the changing orbits of planets when they enter a mean motion resonance. Using a 2:1 resonance, I want to show a low-mass inner planet and a low-mass outer planet being tugged by a Jupiter-mass planet in the middle. I know the orbits of both become increasingly elliptical but I don't know in which direction the ellipse becomes extended. I want to include images of the planets' in orbit, too, so I want my points of periastron and apastron to be realistic relative to the position of the planets in their orbits.
Would the periastron point of the inner planet be near the point of 2:1 resonance where my Jupiter-mass planet and the inner planet are nearest each other, or on the opposite side, as I believe the case is with Neptune and Pluto?
The same question for the outer planet, would it's periastron be closest to the point where it is closest to my Jupiter mass planet, or on the other side?
Illustrating my question, I have an jpg illustration and animation in Flash at this location: Mean motion resonance animation (Flash)