yes, those sizes are factory sizes but you can also use a 255-45-18 front and up to a 255-55-18 rear or the 265-50-18rear as you have but it is only offered by Nitto NT555.
Tires choices that are good thru members here Nitto Motivo, Nitto Nt 555 but the 555 does not perform well in temps under 50 degrees, Cooper Zeon RS3A, Hankook various, A few more others.