Add Multiple Client Fields to WordPress site (MarketPress and Appointment+ plugins)

We have a working WordPress site with MarketPress and Appointments+ plugins. But instead of just entering a name when setting an appointment, we need the ability for the user to add multiple family members and choose from them at checkout. (Like adding shipping addresses, except each appointment will have its own family member assigned to it). In short: - Add field for Name and Grade for the user to choose from when setting and Appointments+ appointment - Allow the user to add new names. This project is urgent (within 12 hours). Please only reply if you think you can do this. Thank you.