Hello there, @Feeney,
I'm here to help ensure you're able to access QuickBooks Desktop (QBDT) from two different sites.
QBDT uses a database file manager to communicate with the company file.
If you're working on the same local network, you can turn on the hosting on the Host computer where the company file is stored. If you're using a server to host your file, once computer has to act as a Host. You must NOT turn on hosting for workstations.
Make sure you have a separate license for each user since you'll be setting up multiple users.
Here's how to turn on Hosting:
For more details about setting up multi-user, you can go through this article: Set up multi-user network.
However, if you're working on different local networks, you must copy your company file using a stick drive. Then, download and install QuickBooks Desktop to another computer. Once done, copy the file every time you use QBDT on each site.
Please keep me posted on the results by replying to this thread. Thank you and I'll waiting for your response.