As a rule we all (pets and parents) go to the vet together. Everyone lives together and shares the same resources, so if one is sick, it seems reasonable to get everyone checked out. If it's annual physical time, well everyone needs one.
If one has a physical issue that is not communicable like a hair ball we still take the family group, for moral support during the trip and while waiting.
The only time everyone does not go, is if the pet does not have a partner (lives in a segregated area) and is going in for a follow up on a non-communicable issue.
Am I just being over cautious/sensitive? Are there medical/psychological issues that make including or excluding everyone from a trip to the vet the better choice?