We looked to replace our Sienna with the new model, but when I learned that the second row of seats were not removable, we dropped it from consideration. We transport multiple single bikes regularly as well, but the seats have to be removed. We also use the the van as a camper (sleeping inside) with the seats removed and lock the tandem to the door handle outside overnight. Again, no seat removal capability is a no-go. If you only ever carry a tandem inside and have no need for seat removal (to haul large stuff - plywood, etc.), then I suppose it’s ok. But I can’t answer your direct question about how a tandem fits since we didn’t bother to test it.