These are all things you should know:
Introducing a New Dog into a Home with other Dogs
Two or More Dogs
Post 8 has a link to "Who Pets my Puppy or Dog" it's what I did it helps to show your dog that you make the decisions and also see "Why Dog Parks are a Bad Idea."
New Dog, Very Challenging
Your lucky that you saw this now and not in 15 to 24 months, not unusual but it needs to stop!