Canine Reproduction Video and Book on Breeding and Whelping dogs by Debbie Jensen for dog breeders and Whelping Supplies needed to deliver puppies.
One of the most helpful websites I found when I had my first litter last year. My advice to you is to go this website and read, read, read. Then google yorkie whelping, dog whelping, and/or whelping in general. Pull up whatever links you find and read, read, read, some more!
Another website I like is Dog Breed Info. Check that one out also.
Good luck with your upcoming litter, and welcome to YT!