Piston twins of more than 6 seats that can be flown on a PPL are thin on the ground. When it comes to aircraft of which I have personal experience, the MEP aeroplane sub 5,700kg with the most seats that I can think of is the DH Dragon Rapide, which manages up to eight plus the pilot. Not sure if some of the bigger Cessnas come in under the weight limit? A C404 can carry up to 12, I think, but it's not the sort of thing generally available for PPL hire. Neither is a Rapide, for that matter. Another (theoretical) possibility is the delightful DH.104 Dove / Devon, which I believe can be configured with up to 6 in the cabin and two up front. Very few of those left, though. The BN2 Islander used to carry, I think, 7 pax max plus one pilot. Again, very rare these days.
In practical terms, I reckon six seats including crew is about your lot on a plain PPL-MEP - unless anyone knows of a larger type still available for hire.