2 people x 2 computers x 2 email accounts each = 4 licences

number of licences needed ? as a pensioner that is a lot of money.

All you need is two Free Licenses. One for each computer.

Register one computer under one email account and register the other computer with the second email account.  This way each computer can have 2 email accounts attached and be legal  as they are registered to 2 different email accounts,    If you need more than 2 attached emails then you will need to buy at least one pro license.