Yeah, a man stands by his word. But I'm only helping, got it? Misaki, you pitch in too.
Literal
Yeah, man [to-に] second-word exists-not. But help-only is-[because-から emphatic-な]. Misaki also do-[imperative-よ].
男に二言はない is a classic set phrase, literally 'a man has no second word', meaning a man keeps his promise once he's said it. It's old-fashioned, a bit macho, and often used half-seriously. だからな with な is a softened masculine 'you get it?'. やれよ is the plain imperative of やる (to do) + assertive よ, a rough but familiar command form.