OK the syntax here really confuses me. Why are there two copulas here?
There are two clauses linked by the particle taw.
mai/taw is used to introduce the second clause because the second clause is an emphatic construction and so has to keep its verb yw in place.
Wait, so that’s three, actually...
So mai/taw is essentially ‘that’, if it introduces a clause?
Yes, if it introduces an emphatic clause - but it is best described as a 'particle', not as a verb.