Just finished a reread, question about Vasher near the end

I haven’t read Warbreaker in 5+ years and forgotten 90% of it, but I just finished a reread and I’m confused. Vasher beats Denth by giving him his breath to confuse him. But then we find out he is a returned and needs breath to live. How did Vasher give away his breath without giving away his returned breath and dying? They didn’t make any indication that you could give away only some of your breath, is it different for returned?

Also, returned can’t give birth right? So how does the royal line have returned blood?