This sounds similar to the same thing I go through on a daily basis, it's almost like talking with someone who contacts me from CL ad.
If a person contact me saying they are a couple, I would ask them certain questions and ask them to both send me a face pic holding a piece of paper with today's date on it. If they can't do that, I will give them details about a meet n greet to meet me at, if they still can't do that just a block button and move on.
I know how to deal with people who stood me up and flakes. They get scared and back off when you hit them with certain words and questions.

