Hi Lisa,

Unfortunately it is normal and recommended to translate the pretérito perfecto in a way that sounds to English speakers like a completed action, in this case "saw / vieron." 

You may already know this but if you look at the rest of the sentence or paragraph, you will notice that the action is set in (this) i.e. the "ongoing present" e.g. this week, this month, this year, or (earlier) this day. For the pretérito indefinido to be used, the action would have been completed in the let's call it more distant / completed past i.e. last week, last month etc.

If it is any help, the "have seen," "have eaten," etc translation is used when you are talking broadly about past events that are still true in the present, like "He trabajado en muchos países," I have worked in many countries.

Yes at first it is confusing to hear the pretérito translation used, but you will get used to it so much that you won't even notice it, because the time context is what matters. Type "marcadores temporales" into the search box at the top of the dashboard page and it will give you some great background to this. Saludos. John