They really don't look too bad, yet. Your pictures of the inside are of the pistons you ask about, and yes, you need to remove them. Their condition will have more to bear on rebuilding them yourself or exchanging them. In a perfect world, the pistons will slide right out. Hook up a grease gun to the caliper and pump them out if needed. If one side pops/moves and the other is frozen, use a C clamp to hold the moving side from popping out and thereby break the frozen piston loose. If the pistons are not pitted, you can probably rebuild the caliper yourself for a good savings if a kit is available. If you need to also replace the pistons, it might be worth just doing an exchange. Check prices. Calipers are not too hard to rebuild. Do one and the next three will be easy
