I need help with outdoor lighting?. I'm hoping someone can help me; I'm an amatuer photographer

Question

I'm hoping someone can help me; I'm an amatuer photographer and will be taking black and white photos at a friends' wedding. It will be close to sunset, near the ocean. I'm wondering how to get the light-framing effect of having the sun setting behind the couple (with the sun being directly blocked by something) without having their faces disappear into blackness. I'm only using ambient light, no flash or artificial light at all. Can anyone help me?