dont worry about ur back tires. just replace teh front two

ur tire has an uneven wear either because of your struts or negative camber(if your car is lowered)

i worked at a tire shop for a few months.

i had a set of nice tires in front w/ lots of tread left on them and 1 blew out and i had to change both of them. what sucked was that i didnt have warranty on them other wise i'd gotten them replaced them from free.

but any ways, if its about front tires, both should be replaced at the same time. because it can set off your alignment and the alignment shop cant do anything about that either.