I only have one so I can only speek of Buddy.
Buddy is smarter than any other dog I have had.
He understands easily and thinks about things before doing them
at times. I can see his brain always trying to figure something out
and most time he does.
He picks up tricks after only doing them one or two times. He associates
the name of the trick with the trick itself and is eager to please.
He understands the names of his toys and will get whatever one you
ask him too. Baby, bone, hedgehog etc. I think Yorkies in general
are very smart dogs.
He is very close to me so I do think he would bite anyone who tried to
harm me.
He is needy and always tries to get his way. Much like a two year old.
When I'm home he never let's me out of his site unless it's after 7 pm
then he chills and dosen't want any part of me until it get's to 8 pm
then hunts me down for his evening snack. How he know's it 8 pm
I will never understand but he does and never misses a night to come
find me and sit up begging for that snack.

Living with Yorkie is very different than living with a dog.
You have to experience it to understand it, I guess.
You'll see