This thought just occurred to me. Do you have the Macbook Pro Firewall enabled? System Preferences -> Security & Privacy -> Firewall. Is it enabled? If it is, try disabling it.
Time to ask a question about your network setup. Wild Goose Chase questions.
You mentioned an Airport Extreme. Is that the ONLY router in the house? The reason I ask, is that if you have multiple WiFi routers (for example because your house is so large, you need more than one WiFi router to cover the entire house, or your house has has 4 floors you need to cover and the structure interferes betwen the basement to the converted attic), you could have multiple subnets which could affect the ability to connect to devices on the other subnet. If you do have multiple subnets, there are ways to address this.
I would like you to download and run "Bonjour Browser"
Run Bonjour Browser on the Macbook Pro (and any other Macs you like). I want you to look for "Remote Frame Buffer" entries (VNC Servers - aka Screen Sharing servers). Click the triangle to show all the systems offering VNC server.
Assuming you see your Macbook listed, click on its triangle to show the IP address and port number. It should be something like 10.0.1.nn:5900. Hopefully you see the same IP address as you think your Macbook has assigned to it (which you can see via Macbook -> System Preferences -> Network -> Advanced -> TCP/IP.
If you are not seeing your Macbook via Bonjour Browser from your Macbook Pro, then there is something affecting your ablity to see the Macbook.