FaceTime doesn't work on overseas call

Three units and some work together while others don't.

1. My MacBook Pro running 10.10.4. located here in the US with FaceTime 3.0 2211

2. My wife's iPhone 5s running IOS 8.4 located here in the US.

3. Son-in-law's MacBook "n" with unknown OS located overseas.

These work well.

(1) can call (2).

(2) can call (1).

(3) can call (2).

These do not work - they ring, show "connecting," but then fail to connect and after 30 seconds fail.

(1) cannot complete call to (3).

(3) cannot complete call to (1).

Firewall is enabled on MacBook Pro.

(1) specs: MacBook Pro (13-inch, Late 2011), 2.4 GHz Intel Core i5, 4 GB 1333 MHz DDR3, Intel HD Graphics 3000 384 MB

I could use some help discovering what I'm overlooking.

Thanks.