One suggestion I can make is to put both dogs on a good strong exercise program.
Best idea Marty. There's an old saying that a tired dog is a good dog. However, one person walking both dogs is not a good idea at all. Should they get into a fight while out or decide to go after another dog, then one person will most probably not be able to control things.
First and hopefully, they are both neutered. If not, get them neutered asap.
Secondly, join an obedience class and take both dogs. Complete the course and do the necessary homework between classes.
Thirdly, make sure they are crated and/or never left alone together.
Fourth, get brother out of the picture. Neither are apparently his dogs and he has no business beating them. Beat him if he does it again.
After the obedience classes are over, make sure you keep up the commands at home. When the family is together, put the dogs each on a 'down stay' and make them do it. Neither is realeased until given the ok command.
Practice the NILIF. (Nothing in life is free) They only get rewarded for good behaviour.
They may never like each other, but if obedience trained, they will look to the owners for direction and that is what you want 100% of the time.
I've shown dogs for over 50 years and prefer males, so most of the time I had a great many males (whole males at that) living in the house together. Never had a fight yet. However, ALL were obedience trained. It does make a difference. And lots of exercise each and every day.
Incidentally, my daughter named her Harlequin Farms after our most favourite Harlequin Great Dane. He's been gone now for 32 years, but still missed greatly.
Good luck.
Lizzie