When using the /team command, people of the same team can attack each others' dogs if the owner is offline (cannot if they are online). Is this intentional;; if it is, is there any way to prevent us from accidentally attacking each other + each other's dogs?

Currently, the issue is due to design limitations. In other words, as of now, I am only able to check if you are allied to the Owner if the owner is available. We are still going to find a way around this as we do agree that the ideal behavior is you not be able to attack other player's Dog even if they are offline.

That makes sense. Thank you for the clarification!

Seems like we have found a way to detect owner ally even if offline.

1.18.42 has been released which solves this issue. Backport will be available soon.