I too agree about the quality of the tire and that bent axles can cause these types of issues.
Either size will fit fine....the 205 is the standard OEM. The 215 negligibly larger, but provides a bit more capacity.
Front tires of a tandem will wear faster than the rears as these "scrub" during turns......the wear of the tire is specific to speed and sharpness of the turn meaning that slow speeds and in particular tight turns wear the fronts aggressively. I trailer a lot so I rotate front to back each season.
Ken
2017 NXT22
2009 24SSV