"Their peacocks are fat."
Translation:Pavones eorum sunt pingues.
You can place the verb where you want, but you have to know that it's more common at the end of the sentence, and you have also to know what it may change the meaning a little, making a word more emphatic than the other one.
But, with "est", it's a special case, it's the copula verb, and it's more common found in the middle of the sentence (or at the beginning). But if you place it at the end, it's still grammatically correct.
So, yes. You can say "Pavones eorum sunt pingues." (more common), or your sentence ""Pavones eorum pingues sunt".