Definitely a NO. Not even funny.......
Please do some research on this subject. There are already too many people who just "want to breed" their dog and don't realize the responsibility there is that goes with it.
Your sisters boyfriend doesn't sound like he understands the importance of this subject either. Education is the best solution...... don't jump into this.... It is great that you decided to ask for opinions and advice! This is a great place to do so........ we all care very much about the well-being of not just Yorkies..... but all little Furkids!
Thanks for asking..... hopefully you will make the right decision.