Could erat be translated as being in this sentence, or ever at all, because to me it sounds better if it was; at least in the context of this sentence.
Atque in exercitu eius plures adulescentes militabant, apud quos erat amicus quidam Publii.
And in his army, many young men were soldiers, among them being a certain friend of Publius.
Also, am I translating quos correctly as them? What’s the reasoning behind that besides because it’s together with a preposition?
I dont see the problem with translating erat as “was”. I think your translation is problematic not simply because you change the tense but that that you substitute a participle for a finite form. It doesn’t sound very idiomatic.
I have a preference for translating “quos” here as “these” but I wouldn’t say that “them” is wrong. I think the translation is just clearer with a demonstrative pronoun. The literal translation of the latin relative would be “among whom”.
I dont quite understand your questioning about reasoning. “Quos” is a relative pronoun referring to “plures adulescentes”.
I found some source online that said that apud quos= apud eos quo. What does quo translate to there? And what does the whole thing translate to at that? Would it be among them which?
And I was asking why quos translates to them/these when together with apud and not as whom.
This could be more of a “sense of the English thing” than anything else. I would see a literal translation of your sentence something like “And in his army many young men served as soldiers, among whom was a certain friend of Publius.” Now, there are different ways of putting that together in English. You could split it up as two sentences, “And in his army many young men served as soldiers. Among them was a certain friend of Publius.” Your rendering is not impossible, but it’s awkward, and erat functions perfectly as the main verb.
As for your question, where did you find “apud quos= apud eos quo?” It doesn’t. I could only find this here:
Melitensis Diodorus est, qui apud vos antea testimonium dixit. is Lilybaei multos iam annos habitat, homo et domi nobilis et apud eos quo se contulit propter virtutem splendidus et gratiosus. Cic. Ver. 4.38
Your rendering is not impossible, but it’s awkward, and erat functions perfectly as the main verb.
Or would it be possible to just translate quos literally (i.e. whom)? Because you have to admit, that wouldn’t sound as awkward as translating it as them. Compare:
And in his army, many young men were soldiers, among them was a certain friend of Publius.
And in his army, many young men were soldiers, among whom was a certain friend of Publius.