I can hardly believe that you have 4 people including an accountant and your basically stating you will be paying cash in hand.
Your time frame on this is ludicrous. Pay even worse as your asking for a total of 5 weeks so thats what £6.42/hr a big 20p over minimum wage and as you keep stating your wanting them to also pay tax and ni contributions from that so its actually below minimum wage.
Good luck with that.