It's prototypical for the horn and bell on only the lead unit to sound off when in an advanced consist. If you want all three horns and bells to work, you can set the addresses of all 3 decoders to the same address instead of creating a consist.
I have several A-B-B-A consists set up as Advanced consists using QSI, ESU, or Tsunami decoders and they all work this way.
When you created the consist, if you selected the B unit as the lead loco that's why its bell and horn are working instead of the lead A unit.
Do they all have the same basic address, or do they have separate addresses but then they're consisted? Which address are you using to run them?
What happens when only one of them is on the layout?
Put each unit on the program track and read back its address. Make sure they're what you expect. It's possible that the installers programmed the addresses incorrectly.
Offhand, I'm thinking that they forgot to connect the speaker wires on the two A units. I would take off the shells and check that if nothing else works.
It takes an iron man to play with a toy iron horse.
Craig North Carolina