We have been having behavioral problem with him since i got him, and we have been working with him this whole time but its just doesnt seem to help and is getting worse

We have come to the conclusion ( he was a shleter dog as well) he has problems with men who have beards, and since my dad does he does nothing but growl and even tried to nip him. And due to me,my fiance and son living with my parents because they watch my son when both my fiance and i have to be gone ( school and work), and my parents are just trying to make it easier for us and since my dad is retiring next year, as he says the house will be ours and just a home base for them, but he is fed up with nothing working, we have been trying since we got him and nothing has worked, and then with one incident where he let my dad pet him under the chin and not even a min later snapped at him when petting him, kinda drew the line for my dad after putting up with it for over 6 months, and with my dad being gone all week, and only home on the weekends, its really taken a toll on him and his love for animals. but he is going to a family friend who is single ( no men at all live with her) and he will have alot of room to run and play and we will get to see him.
I am sure there are people out there who will condem me for it but, at the moment its my parents house and i respect them. my dad has worked all his life and been in the military so i hold his word high in my heart as he is even sad it hasnt worked out but he just doesnt want to loose his love for animals becuase one is making it hard for him.