One advise is to keep monitoring their academic results by contacting their educational institutes directly. If one of your kids is having struggles in his academic life, this should be a warning sign to you that this kid might started to play around over there. In that case, don't give him/her excuses and bring him back home.

Another suggestion is to send your son and daughter to the same country and let them share an apartment together.

or simply, you can send your wife to join them and stay with them there.