Hello!
I would like to help you with VPN configuration. I suggest you to use OpenVPN, it's strong, flexible and good VPN protocol. Can you explain me more about network configuration on your sites? what routers do you use?
About my experience: I have big experience with OpenVPN servers\clients. Experience with variety of different configurations OpenVPN servers, such as serial connection 2 or 3 OpenVPN servers, for maximum security. OpenVPN over IPv6 protocol. I have big experience with network administration and pfSense. Experience with VMWare ESXi, MS Hyper-V, Proxmox VE, Mikrotik, Ubiquiti and some different skills.
My another skills and reviews you can see in my profile.
Hope for cooperation!
Thank you!