ssh port forwarding with permament connection between remote and destination

Solution 1:

One cannot do this with SSH. And such a generic approach would not be a good idea in the first place anyway.

TCP is a byte stream and not a message protocol. This means if multiple clients send messages in parallel, then the messages might be mixed up. The resulting data might start with the beginning of msgA from client A, continue with parts from msgB from client B, the continue with another part from msgA etc.

Thus, instead of a generic approach one would actually need a mixer which understands the specific application protocol spoken and would make sure that the message syntax in the merged data stream is preserved, no matter how the clients send the messages.

Note that this would be different with UDP since UDP is message based. But your use case seems to be TCP.