I would like to point out that the word "apposition" is spelt the way Dantius spelt it:
Apposition.
In your sentence, the three ablative nouns are simply a tricolon of three different nouns. I could also render this as "(et) a tribunis et praefectis et reliquis".
If there were an apposition in that sentence, let's say we'd have something like 'ortus a tribunis militum, comitibus Caesaris (...)', then Dantius' simple rule would apply: The apposition is in the same case as the noun with which it is in apposition.