What would you do in this dilemma?

Yes, this is long but I did read it all! This is another case of someone letting a family member control them because of money! Money and family members do not mix (most of the time)! This gives him controlling power over your partner, as you have found out! Your partner needs to move out, and leave his controlling father. He does not need him to help him nor does he deserve any sympathy from his son! He's taking a trip overseas for goodness sake! That would not generate any sympathy from me!! Sure he might lose his money he has saved with his dad but he can start over with you! I really doubt he will give him the money anyway, that's probably what he's taking the trio with :( Just tell him to accept his losses and to move on! Good luck with that in-law from hell!