Returning traffic from the pool members with a different port

You can use FastL4 profile to sort it out. There's an option called loose-initialization and another one called loose-close. When loose-initialization is enabled, traffic received populates connection table even if connection is not established. This allows asymmetric traffic to go through F5. If failover occurs active connections will still be maintained because Loose Initiation just doesn't care if 3-way handshake has already been established or not. When this setting is enabled it is desirable to enable loose-close as well as BIG-IP will delete and close loosely-initiated connection upon receiving the first FIN from either client or server. Have a look at this article: https://support.f5.com/csp/article/K13558

It's not updated but still good. I'm not entirely sure how's your set up but as Pete said above, you can either an ephemeral listener or create multiple listeners (virtual servers) for returning/outgoing traffic and it should work just fine.