Learn Spanish (Latin America): Se enseña a los modelos a posar con carisma.

This is the core rule of using the impersonal se with the personal a. If we didn't use the personal a and just said se enseñan los modelos, it could look like a reflexive sentence meaning the models teach themselves. To avoid this confusion, we add the personal a. Whenever you use the personal a with an impersonal se, the verb is permanently locked into the singular form (enseña), regardless of whether the noun that follows is plural.

Why are there two different as in this sentence?

They serve two completely different grammatical purposes. The first one (a los modelos) is the personal a, which clarifies that the models are the people receiving the action. The second one (a posar) is a preposition required by the verb enseñar; in Spanish, you always use the formula enseñar a plus an infinitive verb to mean to teach someone how to do something.

Can I translate this literally as One teaches the models to pose?

Yes, that is exactly how the Spanish impersonal se functions here! While the natural English translation uses the passive voice (Models are taught), the Spanish sentence is actually saying One teaches the models or People teach the models. This active, impersonal framing is exactly why we need the personal a to mark who is being taught.