Learn Farsi: این چای از ایران است.

از (az) means "from". Just like in English, it comes right before the place of origin, so از ایران (az Irân) means "from Iran". You will use از whenever you want to say where a person or object comes from.

Is it normal for the verb است (ast) to be at the very end of the sentence?

Yes! Farsi word order usually puts the verb at the very end of the sentence. While an English speaker says "This tea IS from Iran", a Farsi speaker literally says "This tea from Iran IS". This is a great habit to build early on.

Would the word این (in) change if I wanted to say "these teas" instead of "this tea"?

No, it stays exactly the same. In Farsi, pointing words like این (this/these) and آن (that/those) never change to match a plural noun when they are placed right next to the noun. You would just make the noun plural, but keep این.

How would an Iranian actually say this in casual, everyday conversation?

In spoken Farsi, the formal "is" verb است (ast) usually merges with the word right before it. Since ایران (Irân) ends in a consonant, است simply turns into a short "e" sound. So, people will typically say این چای از ایرانه (In chây az Irân-e).