Split traffic between network interface..

You can't do this - at least not practically.

Traffic routing is typically based on IP address, not port, so it would be possible to say 'send all traffic for a.b.c.d over en0 while sending everything else over en1, but you can't limit it by port number.

Should be easy, if you have a spare computer. On that one, set up web and FTP proxy servers. Make it available only on the Airport network. On the first one, in the Network settings for Ethernet, configure the proxies you set up.

If you can find proxy server software that can be configured to send all outgoing traffic through a specific port, then yes. But I don't know whether that exists or not.

Try IPNetRouterX

How I do that? It will work for me

Assuming you have separate router available on each network, like:

en0 - 192.168.1.2/255.255.255.0 with a router at 192.168.1.1
en1 - 10.1.1.2/255.255.255.0 with a router at 10.1.1.1

and a default route of 192.168.1.1, all your traffic will go over en0.

To direct specific destination traffic over the wireless network you use the route command telling it the destination IP address and the router to pass the traffic through.

For example, to route all traffic for 1.2.3.4 through the wireless router you would:

sudo route add 1.2.3.4 10.1.1.1

Now any traffic for 1.2.3.4 will go through the wireless router and everything else will continue to use the wired router.