Strategy: website for travel agency with FileMaker management

[trevix]

After a lot of research, I have not yet been able to understand how to recommend / fulfill my client's wishes.

I created a management software (FMS16 on the client hardware server) for a travel agency, which at the moment communicates with customers with exchanges of e-mails and pdf, automatically generated by FM.
Now the agency would like to allow customers (say 20 max concurrent users) to log in on the internet and exchange all the information, in the various pre-trip and post-travel phases, via the website:
- secure web login, password generation, forgotten password management, etc.
- entry of travel data on specific pages dedicated to the customer
- possibility for the client to fill in personal data
- signing of the contract (generated pdf, which was previously sent via email, downloadable, signed and rechargeable on the website)
- update on payments, advance payment, wire transfer receipt, etc. (no payments on the web site)
- linked pages for traveler's travel data (children, wife)
- list of participants in the trip, meetings, technical notes, departure updates
- downloadable invoice
- travel evaluation form, privacy, etc.

Briefly, all the above and other things.

Almost immediately I discarded the idea of using web direct because of:
- complexity and security in login management
- have a "responsive" website

I then proposed to those who manage their website (currently used only to present travels), to do an ESS synchronization with a website / MySQL on a host, I think it is quite traditional and therefore easy to implement (sigh?). The data to the agency would be local on a second FMS (so as not to have the possibility to corrupt the management FM) that, synchronized with MySQL remotely, would allow to update the tests and documents.

They told me it's not a good idea, because data duplication (FM and MySQL) would make everything more complex and difficult to manage (they do not know FM).

At this point remains Custom Web Publishing. I could not handle the problem, not knowing php, html etc. I find it difficult to find a supplier company that is not clearly biased towards FM or just web design.

The question is: how do others do?
Trevix