Networking issue

Why can't you just connect the MBPs directly to the TC with Ethernet? No point in buying more hardware.

 

You can actually run an Ethernet connection between the two computers without any hardware, but allowing the computers to remain connected to the internet while transferring files isn't possible.

I would recommend using a firewire or USB external to transfer files.

 

What he could do is to setup a wireless access point near the computers. Then connect that access point to a switch, and the two machines to the switch. From there you could disable the WiFi on the two computers and you'll have all that you need. But this is an expensive way to go because you need to buy an additional access point and switch.

Ideally if you're going to be backup the machines via time machine, you should have the time capsule wired to the machines to speed up backups and not kill your WiFi bandwidth.

I'm assuming that the Time Capsule is need the entrance point in your house where the internet is coming in. Thus why you have it there. What you could do is to pick up a wireless router and put that there. Then move the Time Capsule to the machines and use that as the wireless access point. That would give you wired access to the drive of the Time Capsule, and give you WiFi at that same time.

There are a bunch of good WiFi routers out there for around $100. Most of them should work. The Time Capsule already has a GigE switch so there is no real reason to buy another switch, you could just plug both machines into it.