Kepler's 3rd (multiple)

Hi, I am doing a physics project at school, which consists of recreating our solar system (with the sun and only 2 planets, Earth and Jupiter) with Visual Python. Then we want to measure the speed variation of the sun caused by both planets, to determine its period in a graph, which would allow us to find earth's distance from the sun and earth's mass. (In resume, I want to find an exoplanet, from a distance, in a binary system) But I just realized that Kepler's third law generalized (P^2 = (4 Pi^2 a^3)/(G(m1+m2)) )is for a binary system...

I was wondering if any of you know about the equation for a system who has more than one object? I'm looking forward to doing it with the whole solar system if possible.