There's good news and bad news.
The good news is yes, FileMaker is well suited to work cooperatively with many versions of SQL databases, across all different kinds of platforms. It can connect via ODBC using either direct queries or via import / export, and it can use a direct connection technology referred to as ESS (External SQL Sources). So what you're describing is perfectly achievable.
The bad news is, if you're not familiar with FileMaker and how it works, doing an external connection is a mid- to advanced-level skill. This is because FileMaker is ... different. You have to engage in a bit of a paradigm shift to work with FileMaker, because it doesn't work like your traditional SQL database. So your team will likely have a learning curve and will have to do a brain shift to move back and forth between the technologies.
The other good news is that FileMaker is actually easy once you make that paradigm shift. Depending on how much your client is willing to do (and how much he knows about FileMaker), setting up the connections between the two databases is very doable.
On the other hand, it might be worthwhile to look into hiring an actual FileMaker consultant to lend a little advice on the specific project. Not necessarily to do the work, but to give some specific guidance after looking at the specifics of the two systems. You can use FileMaker's "Find a Developer" tool on their web site, or look on places like eLance or Linked In.
wanting their local sql tables to talk with the server sql.
Describe this better.
What is "local"? A server running at the client's premise? What database and what version?
What is "server sql" then? What database and what version? A little later you mention "online version" What's that? A cloud-hosted database? Again: what database and what version.
Since you are PHP developers: what's the PHP role in this project?
Good advice here.
What SQL Database are you working on? What does "not doing it with live sql" mean?
If your new to Filemaker expect some frustrations learning how it works, but generally speaking most problems can be solved.
You were able to read between my lack of understanding of FM and give me a good clear answer of some of the challenges we may face. I am not the programmer, so I will be speaking with my team today about what we need to be aware of and may even consider taking your advice of find a FM a develper to assist in the project.
The local is the Clients ESS communicating with the server sql by way of import/export. Based on what I have read through this forum, doing this "live" (in real time) may cause some issues. I will be having this discussion with my team today. As mentioned I am not the programmer, I am purely doing the leg work, my team will fill the gaps in for me. (Small team)
Yes it is going to be a learning curve, the client has found that most developers here in NZ don't deal with FM. This includes ourselves; however I never turn an opportunity down to learn and the customer is aware of this. Looks like I will be calling on the advice of the community here, or posting in the "Looking for a FM developer for assistance"
Thanks everybody for your contributions.