Hello Jack I would say "This is Jack, and Mary, and Betty". But I'd not say "That is Jack, and Mary, and Betty". "That" seems as if I were indicating a thing rather than a person.
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1.A "I saw two young girls on my way to the farm"
B "that will be Tina and Judy"
3. A "Are there girls in your grade?"
B "Yes, there is Tina and Judy""
4. I would use "is" here