
Is it possible that one of them just can't tolerate the actual sound of the door bell...??? Could you get a cheap pay as you go....leave the mobile number on a piece of card outside....asking visitors to ring you rather than ring the bell or knock the door.....???
A dog's sense of hearing is so much more acute than ours....
I think it likely.....that even each individual dog "hears" noise differently to another....and that different pitches...frequencies etc....... may affect each of them in varying degrees. For instance Our Meg....has always since being a tiny puppy....set up a howling when She hears Cows mooing....or a chainsaw buzzing....Once She starts Her Howling.....then the whole pack joins in Howling..... (I love the sound of The Howling personally.....theres something really pretty and primal about it.....but thats probably just Me.....LOL..... :)
We have four Collies that live in the House with us....Chase....Lotts...Little Tess and Grandma Skye....people that we know well can just walk into the Kitchen.....and they tend to just amble up for a stroke....and then sit down again....If someone knocks on the door that we don't know .....then The Girls may well bark.... but then all line up.....and look back at Me..... to see how I'm going to react
Its possible that one of your dogs intensely dislikes the doorbell....the others KNOW She is going to react to the doorbell...... so move into a position to maybe try and calm Her... they are ALL now also anticipating YOUR reaction too.....and by The Time you actually manage to answer the door it feels like you have run a marathon....you open the door.....the whole pack is relieved that actually there wasn't any threat.....and begin "celebrating" by leaping and greeting....and general group hugs all round.... :)
Now if we were talking about The Electric Gates that lead into Our Garden and strangers approaching them....then yes....that can sometimes turn into a Free-For-All....but again....I feel this is dependent on The Attitude and Aura....being given off by the approaching stranger.....
It doesn't happen very often....but if any of My Collies do bark aggressively at a Human.....then it puts Me on My Guard too.....and to be honest..... I tend to trust their judgement....!
If My Collies don't like someone.....then its unlikely that I would even want them coming into My Property anyway.....! :)