Squeaking brakes do not necessarily mean that the pads or rotors must be replaced. There are other causes for a squeak. If the squeak isn't from the squealer device in the pads when they're too thin, then the squeak is from the steel backing of the pad rubbing against the cast iron of the caliper. Clean them and lube them with a suitable brake anti-squeak lube.
You can look at the calipers and see how much pad thickness remains on the outer pads of each caliper. It is possible, but not very likely, that the inside pads are much more worn than the outside pads in each caliper.
Why replace the discs? I know, they're a wear part, but if they aren't significantly thinned or grooved, why replace them? A shop will always replace them for (a) more profit, and (b) less chance of a come-back. If they aren't thinned or grooved, just sand them with abrasive cloth and clean them with solvent.