Could this literally be understood as 'Sixty are the members of the Assembly'? And therefore why 'oes.....' isn't used in the Welsh, even though it's very tempting from the English!?
That would be used for a question
Where does the "there are" come in, i just translated it (incorrectly) as "sixty members of the assembly".
Mae is the verb here. In this pattern - one concerning the existence of something - it is translated as 'There is/are...':