Do I need CAL for my Windows Server 2016 Standard if it's used only for data sharing?

Hi,

We have a Windows Server 2016 Standard still in trial (a few days left) and I'm wondering if we need CAL for what we do with that server.

We need Windows Server because of FileMaker Server, but no one is directly connected to the server. It's used for file sharing and FileMaker. There's 3 differents user accounts available. Some PCs use user account 1, some use user account 2, etc.

It's working like a charm in trial version but will we need CAL after purchasing a basic Windows Server 2016 Standard licence?

Thanks for your help.