Without a Western Union -the safest way I can think of is to get their bank info and do a bank wire transfer. It would cost about $30-40 probably but you know for sure they would get it. You might be able to get creative using a credit card and a cash advance but I'm not sure how or if any bank or business would go for that there. Barring sending cash in the mail internationally (which I have done successfully but it's a gamble) you're going to need more assistance from your father-in-law.
You could try FedEx or the USPS and pay for the option that provides the absolute most tracking and hope it works.