I understand your concern about the dog and your son. However, I think your h should be the one to bring the down back home to his son. By going to get the dog, you are alleviating your h from his responsibility of ensuring that the dog is returned home to your son.
Call him up and advise him that your son wasn't happy about the dog not being there last night and to please make arrangements to bring the dog home, i.e., even if this means meeting him halfway...but he needs to explain why things went south to his son.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
