If the owners were present and saw it happen, why are the dogs still alive? I'd have shot them right then and there... no questions asked and no second chance.
One dog against any pack of attackers will generally not fare well. Average pit weight is 60-80 pounds. Many LGD sellers (today) are selling LGDs of about the same weight. A true LGD, IMHO, should be well north of 100 pounds and all things being equal, would/should have little trouble fending off and if necessary, taking down a single pit. Since LGDs work best as a team of two or more, I would imagine that an experienced/trained LGD team would be able to fend off a trio of pits. I'm not a dog fight promoter and haven't witnessed any of this first hand... just educated guesses.