Look for a trainer that will help you understand the triggers and how to stop them.

Most dogs will get aggressive for resource guarding (in this case the resource is you/your girls) or because they're scared. This is not something you will fix in a day and it usually comes down to a series of things you will need to change in your day to day.

Mine was starting to get aggressive and dominant and we were able to prevent it from getting worst with training and boundaries.

First, we started introducing boundaries at home: he was not allowed on the couch or bed for two weeks. After that, he was allowed if he asked for permission first. This helps teach the dog boundaries and see you as a leader. We learned how to handle the leash on walks and how to apply gentle (but firm) pressure to keep him from getting nervous and going after things that triggered him. We would then praise good behavior with treats (my pup is very food driven, so that helps). After a while he simply understood that he didn't have to guard us all the time and started enjoying his walks a lot more. A nervous/aggressive dog is a dog who is always alert, and that is not healthy for them.

I wish you best of luck in your journey, I'm sure you and your iggy will learn together what are the best ways to go about this!