Who says some twenty of them fought in this black strife in romeo and juliet?

Answer 1

Lady Capulet in Act 3 Scene 1. She is not prepared to accept the truth of the death of Tybalt from Benvolio, so she makes up a story which is in line with her own wishful thinking about twenty Montagues ambushing Tybalt. The Prince, fortunately, spots her for the frightful liar she is. Lady Capulet is a despicable character, and here she is at her most despicable.

Answer 2

This line is spoken by Lord Montague in Act 1, Scene 1 of "Romeo and Juliet." He mentions that approximately 20 Capulet and Montague family members were involved in the fight.