When I use trusts on drg I typically call 2 DDs and a WHM. I fight one mob so I can get pro/shell from the WHM for 2 of the DDs and myself. After the first fight I dismiss the WHM and call a 3rd DD. I know people will wonder why I don't use a BRD but I just prefer the DD for what I do.

Wyvern AI, in regards to Healing Breath, doesn't take the job of the target into consideration. There are a few things that go into determining who receives the cure. Also, there are two ways to trigger Healing Breath; using a spell or the 1 minute recast JA Restoring Breath.

When attempting to start a HB (Healing Breath) using a magic spell, the wyvern AI checks to see if anyone in the party is below a certain HP percentage. This percentage varies based on the dragoon's support job and whether or not he/she is wearing a variation of the AF helm. Without the AF helm this HP percentage is 33% with a mage subjob (whm, rdm, blm, blu, etc.) and is 25% with subjobs such as pld, drk, run, brd, nin, etc. If the dragoon is wearing the AF helm these HP percentages are boosted from 33% to 50% with a mage subjob, and 25% to 33% with other subjobs that can cast spells.

If the wyvern AI determines that someone in the party is below the appropriate HP percentage to trigger the HB, that person is targeted and healed. If more than one person is below the HP percentage the HB is targeted at the person highest in the dragoon's party list. If the dragoon is among the people below the HP percentage, he/she takes priority and receives the HB. Apart from the dragoon getting the priority breath, the party members below the HP percent are healed from top to bottom in the dragoon's party list.

Dragoons gain the JA Restoring Breath at level 90, which allows a dragoon to trigger a HB regardless of whether or not any party members are below the fore-mentioned HP percentage. Since I don't use this JA regularly, my knowledge on it's behavior may not be as accurate. I do know that if the JA is used and someone is below the HP percentage, the AI behaves the same as I stated earlier (dragoon gets priority if he/she is below the percentage, followed by other members under the percentage in a descending order on the dragoon's party list.)

I normally sub /mage so I don't rely on this JA as much as /DD dragoons. I usually reserve it for emergencies when I risk getting a spell interrupted if I try to cast a spell to trigger HB or if I'm silenced. Therefore, the next statement may or may not be accurate. If the JA is used when no party members are below the HP percentage (which I never really have any reason to do unless I hit the macro accidentally) I think that the AI targets the party member with the lowest HP percentage.

Sorry for the length. The reason I made this thread, just to recap, is that the wyvern AI follows this pattern with trusts in all areas except the one that is most important to me. The wyvern's master is only healed if none of the trust party members meet the requirements to receive HB. Every trust must be above the HP percentage before the dragoon can hope to receive a life-saving heal.