Access to more than one internal server with the same serivice

Do not create a NAT Rule for RDP. https://www.sophos.com/en-us/medialibrary/PDFs/technical-papers/sophos-rdp-exposed-the-threats-thats-already-at-your-door-wp.pdf

Let's assume that, another service, may xxxx port.

Its not possible. Any firewall product cannot figure out, where to route. The static principles are applied. You have Source, Destination and service to figure out, where to route. 

see, I have static IP (No IP) that fixed in my ISP Router, I opened a port in that router as following: wan=6666, lan=3333, ip=192.168.1.2 (WAN port of sophos).

the router connect to sophos WAN port, and I created DNat rule for 3333 port, all thing work ok, but I have 3 PCs use the same port 3333, I want to open ports in router as 7777, 8888, and every one go to the specific PC with port 3333.

I wish that be clear.

BR

Sami

It is bad practise to have RDP open to the internet. Even when you use non standard port numbers. Use for example SSL VPN to connect to your LAN. Users can then connect to the required internal ip adresses or use the internal DNS server.

I want another port not for RDP service, I mentioned it for example,

i have 3 Devices with the same port, want to access for these three from outside

Have you tried the WAF functionality? Documentation states it acts as a reverse proxy...
I'm not sure if it will work but it might be worth giving it a try.

Make three webservers, each point to the respective internal machines.

Make three incoming rules listing to something like path [1|2|3].my.domain:portnumber
At first avoid as much protection as possible just to test the mechanism and the rules.

(just an idea i had...)

Thats possible. Simply change the port as you like. Network devices can filter based on source, destination and port to apply a NAT rule. If this is unique, it will be applied to the matching traffic.