You do not say the make or model of your phones - but no matter.
These phones have batteries and internal charging circuits - my guess that the broken ones have no power to make them work.
Can they be repaired? - Very probably but not economically - cost of repair will far exceed the cost of a new phone.
Do you have to buy new ones? - That's down to you and your available budget.
Amazon offer three Panasonic phones for under £50.