Front seats in the Tribeca are wide and firm, with nice proportions and bolstering. Lumbar support is adjustable for both the driver and passenger, and it's easy to find a good driving position—although the lack of telescopic steering adjustment could prevent some from getting comfortable. One issue for some taller, lankier drivers is that the curvy instrument panel design tends to limit knee space—and potentially comfort, on long trips.
In back, the second row slides fore and aft by eight inches—and split 60/40 for longer cargo—and once adults slide it back they'll find enough space to be comfortable. It's a bit flat and not tremendously comfortable, either. The third row, though, is a bit hard to get to (though there are grab handles) and nearly unusable if the second row has been moved back for second-row passengers. You could end up with a balancing act where no one's happy. Fortunately that third row folds flat and expands cargo space when it's not in use.
The Tribeca has a firm but smooth and controlled ride, and an interior that's a step quieter than what we've become accustomed to from Subaru.