Jack, coming from a fallible decade-long Hindi learner, "Kaun hai?" can only mean "Who is [it]?"
To get these other sentences, you'd need to write "Ve [log] kaun hain?" = "Those [people] who are?" = "Who are they?"
"YEH kaun hai?" = who is THIS/he/she? (subject is near you).
"VAH kaun hai?" = who is THAT/she/he? (subject is not near you).
"VE kaun hain?" = Who are they [and] Who is s/he? ---> Ve is the plural of Vah. Plural is used in Hindi to honor the subject by literally speaking about them as if they were "more than 1" person.