Need a complex booking system with paid subscription login

I’ve been asked to help rebuild a website for a babysitting agency (I’m starting to think it is a project that’s more trouble than it’s worth though). I’m after a plugin, or set of plugins that will allow for the following:

– Customer fills out a membership form, picks how long they want to subscribe for and the payment is handled by paypal.
– The customer is then directed to a booking form – only subscribed and logged in members can access this booking form.
– Once the form is submitted, a request will then be automatically sent out to all of the babysitters they have on record containing basic information (ie date, time, number of children and suburb) via email or text message.
– The first babysitter to respond will then be booked for the job and sent the details for the job (extra info like allergies, emergency contacts, names, etc)

I am aware of a few good booking plugins but non as far as I can tell that will allow for “staff” to confirm their availability on a first in first serve basis…

They want the whole process to be as hands off as possible and want to spend as little money as possible on the whole project (hence the more trouble than it’s worth!!). I’m currently in the process of trying to talk them out of an external service which can be embedded in to a Weebly site (because it doesn’t exist!). They are adamant that they want to use Weebly, purely for ease of use, so I need something that will work for technophobes!

Any suggestions appreciated! Otherwise I’ll just tell them to find a web developer.