καὶ οὐδεὶς ἔτι ἄνευ Ἑλλήνων εἰς πόλεμον καθίσταται, οὔτε ὅταν ἀλλήλοις πολεμῶσιν οὔτε ὅταν οἱ Ἕλληνες αὐτοῖς ἀντιστρατεύωνται: ἀλλὰ καὶ πρὸς τούτους ἐγνώκασι μεθ᾽ Ἑλλήνων τοὺς πολέμους ποιεῖσθαι.
they have learned to wage war with Greeks against Greeks. This appears to be wrong in this context.
they acknowledge that they wage war with Gr against Gr. this is oratio obliqua and it seems to be the best interpretation. The translation in CGCG and on Perseus is: but even against Greeks they recognize that they can conduct their wars only with the assistance of Greeks. Where does ‘can’ come from?
they have decided to wage war with Gr against Gr - wrong as well.
τοὺς πολέμους ποιεῖσθαι is not oratio obliqua. It’s what CGCG calls a “dynamic infinitive”. See 51.8, “Verbs of practical knowledge.”
The translations are not literal, but they are within the possible meaning of the Greek. In the CGCG and Perseus translations, “can” is inferred from ἐγνώκασι: “Even against Greeks they have come to the realization to conduct war with the help of the Greeks.” In other words, even against Greeks they have come to the realization that they can’t conduct war without the help of Greeks." A more literal translation would perhaps be “Even against Greeks, they have learned to conduct war with [the help of] Greeks.”