People will need to know various things like how many bass buttons,(usually 24, 48, 60, 72, 90 or 120) how many right hand keys, any voices -these are normally tabs on the front of the instruemnts.

The condition will also be important -if they've been kept in a damp loft they may not work properly and notes might stick, the condition of the bellows is important as well. You really need to find someone who plays to give then a go and see what kind of order they are in. Anyone who buys one will want to try it first.

Do this before you think about asking a price.