Extremely VIOLENT behaviour after owners were away on holiday - PLEASE HELP!!!

Question
My sister and her husband went on holiday for 3 weeks, while I babysat the 2 Jackies - short legged(both female, from the same breeder, but not the same litter). The 2 have contrasting personalities, Maggie is hyperactive and runs around all day without stopping, chasing everything that moves. Droopy is quiet and sedentary. Maggie always dominated, and lately started bullying Droopy. However, since my sister's return from holiday, Maggie started to violently attack Droopy, drawing blood and causing serious injury, even biting my sister's husband so badly he needed medical treatment.

My sister is very loving towards them, but very strict about them getting treats. However, for the 3 weeks that I looked after them, I spoiled them by giving them treats (Beeno biscuits) about 4 - 5 times a day.  I'm a very soft hearted person so I don't think they saw me as the leader of the pack.

Did I mess up their hierarchy by spoiling the dogs? But most important of all, how can my sister establish peace in the home? (at the moment they are kept separately because if they come into contact with each other Maggie immediately attacks.

PLEASE HELP!  My sister loves these dogs as if they were her children, and the current situation is causing a lot of distress.

Thanks in advance
Hannah

Answer
Hello Hannah,
No you didn't spoil the hierarchy, but your sister definitely has to re-establish some rules and order in the house. You know what they say...."when the cat's away, the mice will play".  
The dogs are also displaying some anger because they were mad that your sister went away and left them; and now that she's back....they are going to make sure she knows just how much it bothered them that she was away.
It sounds like Maggie doesn't want Droopy to get any of the attention what-so-ever, so she is acting out violently.
This absolutely can not be tolerated. Your sister and husband have to reinforce the original rules and restore order in the house. If Maggie needs a muzzle, they should put one on her while laying down the ground rules. Tell your sister to give lots of attention to both dogs individually and let them know she isn't going anywhere.
This happens a lot in dogs who are boarded for a while. My own dogs (would never bite me) but ignore me and argue amongst themselves when I return from vacation. My mother watches them while I'm gone and like you, she spoils them very badly with the treats. Treats should only be used when the dog has done something wonderful. They are used to reward GOOD behavior. They become out of control little beggars and expect a treat everytime she walks through my door. Your sister has to start over from the beginning now, re-training them to respect her and eachother. If they are way out of control I would suggest a professional trainer to come in or she could buy THE DOG WHISPERER training videos for some excellent tips.  Don't feel bad, you were only loving them, and a good lesson has been learned :))
You can't give treats for no reason, the dog MUST work for it. It's in their genes! Best of luck to all of you!!!
Take care,
Carol