They'd only appear like Ice Climbers due to being a duo, but they'd function more like Olimar & Pikmin, where the latter follow the former's every move. Nana follows, but also fights. Diddy and Dixie would not fight simultaneously: one is always following—and only following—the other. It'd be no different than Sheik and Zelda being separate entities wherein one followed the other (and was invulnerable), and the transformation special would switch which was being controlled.
The Diddy/Dixie duo would function identically to Zelda/Sheik, but borrow the duo resemblance of Ice Climbers with the following A.I. of Olimar & Pikmin.
The Diddy/Dixie duo would function identically to Zelda/Sheik, but borrow the duo resemblance of Ice Climbers with the following A.I. of Olimar & Pikmin.