Well...I noticed no one had an answer - and neither do I
- but I have dogs on all sides and my girls really don't bark when they hear the others barking -
BUT...if something is going on - Like Lawn Dudes - or Cable guys...Meter Men etc....then ...they bark their butts off. Great little Alarms yorkies are.
I would just see how it goes and IF you see your yorkie trying to join in for no reason....just take appropiate measures to stop the barking....you can read lots of training info on the net.