Welcome to YT ! I am sorry about the loss of your neighbors Yorkie. I have been feeling guilty by not letting my 5 month old puppy play outside, because of the heat. I am now glad that i had made the right choice .
Considering the fact a dog's normal body temp. is 101' it would not take long for the dog who is full of energy to over due it in hot weather. It is a shame that it happened.
I can't wait to see pictures of your Yorkies. 20lbs is a big Yorkie
