For networking purposes, they all must be part of the same workgroup and have unique IP addresses. The IP address part should be pretty easy if using broadband router.
My first thought is to check the firewall. If file and print sharing is not configured it will not allow the PCs to see each other.
As far as remote desktop, I suggest setting up an account at Logmein.com. A basic account there is free and will set up a secure, encrypted connection to your PC from anywhere. This is how I connect all of the time and I am a Network Security Administrator.
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