replacing 2 of 4 tires on a TT question

I have a 30 ft TT (7500 GVWR, though I'm not usually over 6K-6.5K lbs) with 4 Maxxis ST205/75R 14 LR C tires (all 4 always at 50 psi per specs). The front axle had 2 Maxxis from 2012, and the bac...