when i apply the taurus firmware to this cluster will it only upgrade the 205's without trying to upgrade the 305's?
No, if they are within the same cluster you have to provide both Software Versions before you can upgrade.
As shown in my attached picture you have to provide the Instant Cluster both Software versions Ursa and Taurus from the same release before you can upgrade the Cluster. I won´t Upgrade only one type of AP.
How do you manage the Instants? By Instant GUI, AirWave or Aruba Central?