Can he take them both on? If i recall correctly,he wanted Zamasu to kill Trunks bulma and mai so goku and vegeta can get angry and release more power.Does this imply that he is much stronger than them?
No, Black will probably get beat by those two. As for Black telling future Zamasu to kill Trunks and the others, that's because Black planned that clones thing which gave him the advantage over the Saiyans.