Welcome to YorkieTalk. I hope you are able to find your pup. I think your sons would love one. Each pup is very different regarding temperament, and early socialization from a good breeder makes a big difference. They can also evaluate temperament and help match one to your family.
I love Morkies and Yorkiepoos, but if you have a specific look in mind, you can't reliably pick what breed they will resemble more. If you are like me who hopelessly falls for your pups, it won't matter. My sister had a Yorkiepoo who looked much more like a poodle.
I agree with Wylie'smom about Biewers. They are supposed to have great temperaments. The pup in the thread she attached is a special pup from a great breeder. You might also try looking at Yorkie Haven Rescue, a really wonderful rescue.
Yorkie Haven Rescue