Hi,there you have it!!!!!!! you said the middle one starts first then the youngest follows and then the oldest,its obvious the middle is the top dog and then the youngest and then the oldy.Having more than one dog is a challenge for anyone.You learn so much dog phsycology (spelt wrong )
and how they work with each other.When one starts then the rest follow.We had the same with our 3 GSDs,the age between them were 2half yrs then a bro and sister togeather,boy they were a hand full but what fun!!!!!!!
The water bottle is a good thing to use UNLESS ofcourse they love water as ours did!!!!!!
The hosepipe,paddle pools,you name it they LOVED it.
We also had a 19yr old westie and they all took lessons from her also!!!!!!!!!!! when she barked the 2half then barked and then the pups thought...........ok its my turn,
However as the westie was 19yrs old any noise be it loud/soft startled her and i think sometimes it was just a startled /scared type of bark but it didnt stop the others from joining in.You try whatever it takes and still sometimes it backfires purley because you have more than one dog,obviously its alot easier when you have just one dog but if you manage to stop it then its a bonus.I guess it would be easier for you to do one at a time but if they all stay togeather then what fun you are going to have.Good luck!.Regards.