Question: I was watching an Instagram video posted by Woody and Kleiny account <https://www.instagram.com/p/BqxY4lflIKQ/> and here is a sequence of it:

A: Knock-Knock

B: Who is it?

A: It's the Police

B: What do you want?

A: We just want to talk.

B: How many of you **are** there?

A: There **is** two Sir.

B: Talk to each other then.

**Question**: Why it is right to say there is two, instead of there are two?

**Update**: I didn't recall it had subtitles. Know I am seeing that was *there's*.

Answer: 
For many people *there's* is an invariable form, irresepective of whether it is introducing a singular or plural noun phrase. 

*There is* is less common in this context, but you sometimes hear it. 

It is non-standard, but quite common.
That seems to be a "knock, knock" joke, one of a large class. The one you've quoted doesn't seem very funny, but maybe you haven't quoted the entire conversation. As Michael Harvey said in his comment, "There is two" is uneducated usage.