I recommend Fortinet Fortigate devices, “You can have up to 100 concurrent VPN users. The FortiGate 60E can handle more than 25,000 new sessions per second and more than half a million concurrent TCP sessions.”
Once you have static IP addresses, and you have configured your required firewall settings for any devices that need such as VoIP phones or anything hosted internally.
Click here for a YouTube video showing how to configure the site to site IPsec VPN.
This hardware would also give users the ability to have users connect to internal servers remotely, but that will require some more configuration.