Maximum PC

Hi,
Let me begin this by saying that I am not a networking expert and am a huge noob when it comes to it.

I have a business that I want to run better by creating a relational database. The thing is that in order to be as efficient as possible, clients and my contractors who live anywhere and don't commute to work at my location need to be able to access it and make changes to the data at any time. Therefore, I've been thinking about how I can enable this since November and seeing as I am a novice at networking, I have had trouble following the technical explanations of certain solutions and therefore don't know what the best one is. For a relational database to work properly over a local network, the users have to be able to send and receive the new/changed records in real time as others are doing this. This requires constant updates of the DB data files which is possible in a local setting.

From what I gather in casual conversations, websites, and forum posts here, I have a few options (although I'm not even sure if they are options given the requirements of relational databases):

VPN: from what I gathered, this may not be a smart idea since I think if my customers leave the connection open and browse the web, their history registers as under my network. This can be bad if they decide to pirate software through my network.
Hamachi (https://secure.logmein.com/US/products/hamachi2/): This seems good but I really don't know how it works (since I don't really understand the technical language).
SSH: Maybe but I heard it is an old protocol.

In any case, I would prefer to buy a NAS to hold the database (Synology) but if what I want to do requires a server, I suppose I can buy one if it is not too expensive. If you guys can help me, I would appreciate it. If you just want to point me in the direction of where to search google that would be great! Anything is awesome. After I figure out what I want or at least my options, I plan on hiring someone to explain and educate me more if needed but I think I have to know a little before I hire someone so I don't pay an arm and a leg for the help.

Thank you!

You mentioned the database and then jumped to discussing the necessary plumbing, but left out any discussion of what interface you intend to provide to your users.

Presumably your users will not be directly accessing the database, but only indirectly via some application. It's not clear to me why your application isn't web-based (http/https) like millions of others. That would completely eliminate the issue of VPNs, SSH, etc. Or should we assume you're using something more traditional or old school, perhaps a client/server application based on Windows that you intend to distribute to your users? In that case, I can see where you would have to find a means to bring this together over the internet.

I just want to be sure we have the complete picture here before perhaps heading down the wrong road.

Thank you for your help in narrowing the discussion. I was under the impression that relational databases only encompassed those created by programs such as Lotus Approach, MS Access, LibreOffice Base, etc. I plan on creating a database either using LibreOffice (since it is free for my clients to download) or Approach (old school and therefore less likely but more robust).

The reason is that I'm not a programmer but I don't want to spend a lot of money paying someone else whenever I have to fine tune the database based on feedback.

Thanks!

Apologies for bumping this. I really was hoping to at least be pointed in the right direction. Can anybody help?