Assuming ISP gives only 1 external IP and you have few devices that use this IP
That doesn't happen. There's a network address translation in between. Every device has its own IP address.
That NAT device won't just "randomly" forward things to the devices it hides. So, only the NAT device (which you call "router", but it's really not a ...
They can't track you via RDP. that only makes sense for servers you connect to using RDP.
Websites will usually see the IP address of the VPS, but browsers are very leaky when it comes to user data: for example, WebRTC tends to leak your local IP address.
Your browser will probably leak the language of your system.
Not many places that speak Farsi…
A sophisticated adversary able to observe traffic can indeed differentiate different users using the same external IP by analyzing TCP sequence numbers and through timing analysis.
They will be able to draw conclusions such as "The person who visited XXX site also visited YYY site".