Who did what now?

Here's a fantastic title for a seminar: 

The 5 Most Common Mistakes That Parents Make Who Are Estranged

Perhaps one of the mistakes was poor grammar that hindered their ability to communicate. Generally when you have a noun ("parents") and a subsequent description of that noun ("who are estranged"), you don't split them up. When you do, you risk confusing sentences like the following real-life example:

I overheard one customer talking about her dog that was outside with a barista.

You would think this sentence is saying that the customer's dog was outside with a barista because that's exactly what it says, but you would be wrong. The sentence is saying that the customer is talking to a barista about her dog and her dog happens to be outside. I know. It's absurd. But that's why you don't split the noun ("dog") from the description of said noun ("that was outside").

This all goes back to my Golden Rule of English: if it sounds stupid, it's probably wrong.