I have to disagree with posters above who suggest that this is a matter of preference. "This is Scarlett and Isaiah" only makes sense for the name of a show because it is a title. As in, "This is All the King's Men." Which would be different than saying, "All the king's men are soldiers at heart."
Even if it sounds odd to the ear, one should be introducing multiple friends with the verb are. As in, "These are [my friends] Fred, Kerry, Joan, Dan, and Ryan."
The rule for compound subjects is that when the subjects are joined by “and,” the verb agrees with the pronoun “they.” This is not the case if the subjects are joined by "or," "neither," or "nor."
Title of a show: "This is Scarlett and Isaiah!"
Introducing friends: "These are Scarlett and Isaiah."
Using "or" as a coordinating conjunction: "This is either Scarlett or Isaiah on the phone."