Hello & Welcome to Just Answer,
Sorry to hear of any issue you are having with your phones.
To help you with this issue, and see if this is possible, may I ask:1) The Model Number of the EACH of the Main Base Units you are working with? Those models should be printed on a sticker on the bottom or back of the each main base unit and START with KX-TG.
2) Are ALL of the handsets currently WORKING well - with their current base unit?