Getting from Florence to Radicondoli, province of Siena, Italy

Hi, would anyone know what is the easiest way to get from Florence, Italy to Radicondoli, Province of Siena and back to Florence? The problem is in our luggage and the number of people. Based on our research even if we rent a big (by Italian standards car), all 4 of us with our luggage would have problem to fit in. Two of us can travel by train, but then there is other too much hassle to get to Siena as its almost an hour away from Radiciondoli. Any suggestions? Thanks,
Alena