Why would my Great Dane 11 month old attack someone?

I am wondering I have 5 Great Dane 11 month old puppies and they have bit my neighbors older sons, I don’t understand why they would do that. However, it’s always been when I was laying down resting and they have been over to our house helping my husband outside doing sonething, and either they have come in my house announcing themselves, or this last time my husband was with the oldest son and husband went stand by bedroom door where I was taking nap and resting they were all laying down with me when they suddenly got up next I heard is someone screaming and dogs going crazy. By the time i could get up and figure out what was happening, i yelled stop, they did but it was too late. The son had already been bitten.
I know they are very protective over me, I could bring people in and nothing happens.
Does anyone have advice or understanding why this happens and what I could do to stop it.