VPN site to site

By having 2 firewalls can I have a device/ devices be permanently on my local network?
If yes, can I choose specifically which devices are tunneling to a different network?

For example I’m using a SIP base up intercom and I’d like it ring my desk phone at my office.
Right now I need to pay a license to set either sip device to make a call to my phone.
But if it was on my local network I could have done a direct IP call which has more features.

with site to site, you should be able to see all the devices from both sites (if they participate in the site to site). See this article for more examples of what you can do https://help.firewalla.com/hc/en-us/articles/5515850433683-Firewalla-Site-to-Site-VPN

Is there a limit to how many devices can participate in site to site?