Event+ Extending to set a Child and Family Price

I would like to rename the existing Fee: box to Adult Fee (which I have done) and add a Child and Family price when Adding a New Event and then when user books for an event, I'd like them to choose how many Adults, Children and Family (which would equate to 4 tickets) tickets they want.

The number of tickets available should reduce by the sum of the Adults, Child and Family tickets ordered and the price to pay should be the qty * the number of each type of ticket.

In theory it should be straight forward to adapt the code slightly to add a few extra fields on the Add New page and on the booking page, add the extra fields and add the tickets/price together for the correct totals.

Can you please point me in the correct direction by telling me which php script deals with the Add New functions in the Wordpress editor and also which scripts handles the actual customer booking form.

Kind regards

Andrew