Well, you can start by saying they are all piano accordions made in Italy in the 1950s or 1960s.
List them by maker, add all have 3 voices
(except the Marco, which has two voices). Add the number of treble keys and bass buttons. Add the keyboard lengths (outermost edges of outermost white keys).
Add weight (in lbs or kilos).
Add number of treble and bass couplers .
Include at least one clear picture of the front and the back.
Sound all keys and buttons pulling and pushing: mention any ( numbers) not working properly.
You can also list on Facebook.
Think of a number, add $50 .
Be prepared to consider offers
List!

Good luck!