From the point of view of the seller:
We are required to ship to the buyer's address (either on eBay or Paypal and yes there are several reasons they might be different).
If the buyer reports that the item is not delivered withing 45 days, she can get a refund unless the seller can prove DELIVERY to that address.
The buyer cannot add a foreign address to a Paypal account.
Since shipping to Vietnam is likely to be slow, and I suppose that is the reason you would like the more direct shipment from seller to recipient, the seller is in an awkward position.
All in all, it would be best to have the item shipped to you. It will arrive quickly through Canada Post/USPS and you can then repackage and reship it. You can even add your family's address in Viet for the easy use of the local postal workers.
BONUS: you can inspect the item and be sure it is as described before you send it on to your family.