I_am_on_Saturn wrote:
Is Sun positioned at the center of the elliptical orbits of all the
planets?

No. It lies at one of the foci of the elliptical orbits. To
describe the shape completely around the Sun, you need two numbers --
the nearest and farthest points, for example, or the distance across the
ellipse's major axis and the ellipse's eccentricity. (Describing the
*position* of that shape in space is somewhat more complex.)

If not so, what is the relative position of
Sun relative to all the planets?

It's massive enough to be considered the center of mass of the entire
Solar System -- but it doesn't lie at the center of the elliptical
orbits. The ellipses all have their perihelions (closest points to the
Sun) at different points around the Sun, and the planes in which they lie
are tilted with respect to one another.
--
-- With Best Regards,
Matthew Funke )