Oh, I see what you want to do. So, what you want basically is an orbit around Kerbin that has the same period as Kerbin's orbit around the sun. (This way, your ship makes one orbit around for each orbit or kerbin around the sun, thus keeping all three in the same relative position). I just tried solving the orbital period equation for that period, and assuming that a) the data in the ksp wiki for the mass of Kerbol and Kerbin and Kerbin's orbital period is all correct, and the gravitational constant is the same in game as it is in the real world, and c) I did all my math correctly, then you would need a circular orbit at about 4,342,000,000 m around Kerbin, which is well outside of its sphere of influence. So, the best approximation you can hope for is what others here have suggested: take them into a Kerbol-centric orbit that matches Kerbin's orbit, just ahead of and behind it.