Which propane tank are these? Need to replace.

If the tanks are leaking soapy water will show the spot. I would do this before you replace. You can have them re-certified at a commercial propane dealer and leak checked for that matter. I would do this before just buying new.

BTW if the regulator is also 10 years old I would replace. If you have a choice I recommend Cavagna brand. amazon

And yes it looks like standard 30 pound cylinder.