1990 Camry brakes problem

I have a 1990 Camry with 130k. The right rear caliper locked up a year ago when I replaced the pads, now the left rear is locked up. I am going to replace it, what are the recommendations on also replacing the flexible lines? My present ones don't show any signs of wear, other than rust on the fittings. They are a little pricey. Do I have to bleed all the other calipers after replacing the one? Also, why do calipers lock up and is there anything I can do to make them last longer? I do understand that 14 years/ 130k is a long time but I am just curious.