I believe they have a good shot a winning. Yamcha really won't help much, and I think Piccolo could take him out with one or two good melee hits in fact. It's Krillin and Tenshinhan combining their knowledge and skills that would ultimately lead to Piccolo's demise, I'd say. Individually they're rather far from him unless I nerf Piccolo a bit, but together they're a formidable force. A Kienzan and Kikoho combo would be devastating.
Of course, Piccolo's no slouch. He's probably just as skilled as them, if not more. He could just as likely take them out without a whole lot of trouble.