How can I "merge" two networks together?

I have two remote networks: One in Singapore (with a Static Public IP) One in Philippines (hiding behind NAT)

In the Philippines network, I have devices such as an NVR, Backup NAS & etc. In the Singapore network, it's where I am based and everything is at, main NAS, Website Hosting Servers & etc.

I would like to be able to access my Singapore network and all devices within when I'm in my Philippines network and vice versa. However, having the Philippines network

If I choose to create an OpenVPN server with my Singapore network, The issue would be that I don't have a router that would be able to facilitate the connection, furthermore, I'm not sure how the port forwarding would go about so that I can access the Philippines NAS & NVR.

I understand that my NAS (Synology) and NVR (amcrest) has first party software to allow connections to the cloud, however I do not wish to let these devices be reachable through the cloud for my own privacy reasons. I would also like to utilize LAN capabilities such as ftp and like DLNA from my Singapore NAS to my Philippines TV.

I am able to afford Raspberry Pis if it helps.

Thank you