female boxer fighting with other dogs

Question
I adopted a female boxer 1 1/2 years ago not knowing her history excpet that she was with a elder couple and she was too high energy for them.  I have 4 children 15,14,12,6 who love their dog, Dolly.  Dolly is about 3 years old.  She is very good in the house, playing with the kids and listening to all the rules excpet when she is around other dogs.  We brought a kitten home and she loves it and shares her food and sleeps with it.  We live on a ranch next to my parents and brother.  My parents have a male beagle that is Dolly's best friend.  My brother has a female lab that Dolly fights with anytime the lab comes to my house.  Dolly never goes to my brothers house ;she knows she is not welcomed. All the dogs have freedom and go the my parents house.  they love playing my kids and having fun.  But there is always a dog fight and my brother said he is afriad Dolly is going to kill the lab.  Dolly goes for the throat and doesn't release.  It takes 2 grown men to pull her off.  My brother also is afraid she is going the hurt a child.  She has never growled, barked or shown any negative signs toward a person.  I have challenged, tried to make her mad, pull her ears and she just cowards down.  How do I get her not the attack other dogs and should I be concerned with Dolly and children.

Answer
No, you do not need to be concerned about her harming the children or people. Boxers love children, and if she hasn't been aggressive toward people, she won't start now.

Liking the Beagle and kitten is a good sign, so disliking the Lab is a sign of "alpha" challenge.

Apparently, Dolly feels threatened by the Lab, and is aggressive by nature, protecting her alpha position and territory.

This can't change. Just as in people, personalities clash. Dolly's and the Lab clash.

Keep them apart. That is your solution.

If you insist on trying to train them to be "friends" or at least civil, then it will take hard work, determination, and consistency by you and your brother both.

Leash Dolly and the Lab both. You and your brother bring them together on neutral territory. When they show signs of aggression toward one another, tug the leash, verbally reprimand them in a stern voice, using easy to understand commands.

You can also use the verbal noise "uh-uh" (like the no-no sound you use with children) and then verbally reprimand. The sound is a signal.

You could buy two whistles, one for you, one for your brother. Use the whistle the moment the bad behavior begins, as a signal to the dogs, as you tug their leashes, then use the stern voice and verbal commands.

Continue this. It is a sound recognition to their bad behavior.

Once they begin to obey and stop the aggression, treat them with a special treat they normally don't get. Keep that special treat as the special training reward treat only.

Practice this leash-whistle-reprimand-treat (for obedience) training every day if possible.

Don't exceed more than 1 hour of training per session. That is to keep the dogs' attention on the issue and training and not wandering off.

Let me know how this goes.