Wordpress Plugin Development

General information for the website: We sell holidays and travel
Kind of development: Customization of existing website
Description of requirements/features: We currently have a plugin that was developed for us to handle client Booking Authorisations prior to them making a booking.
The idea is that the agent making the booking completes a preset number of fields containing all the holiday details, dates, duration cost etc as well as a section where they agree to terms of booking etc.
The agent will then send the client a link to the form (live web page) where the client can complete their own personal details, full names, dates of birth etc etc and tick boxes to agree to all the terms.
Once the client has submitted the information, the agent can check back through wp-admin that all fields have been correctly completed prior to making the booking.
The current plugin has become outdated and has some bugs I expect following WP and theme updates. We would also like the client facing form to be more pleasing on the eye.
We also have some challenges around multiple users logging in at the same time and causing conflicts and data not being stored in the forms.
The current plugin can be shown if needed to get an idea of what exactly is required
Similar urls: http://explorertravel.org.uk/travel_booking/sarah-edwards
Extra notes: