Shooting couple portrait with Nikon 60mm micro?

I'm doing a couple portrait shoot, one is embracing another from behind, but the person behind is a bit blurred. I'm standing about 6 feet from them, using Nikon D90, "A" mode with iso 100.

How do I shoot them both clear?

You can use your f/stop priority and set the f/stop for anything like f/8 or smaller (f/8.f/11.f/16.f/22.) The higher the number the more depth of field you will have. Or the distance that is sharp increases as you move from f/8 to f/22.

I really don't recommend shooting a portrait with a macro lens. Don't you have the lens that came with the camera? Like a 28mm to 55mm. I would use the 55mm setting and a small f/stop. Use a tripod also, plus a high enough ISO to avoid camera shake or subject movement.

Have a deeper depth of field - larger f number like f11 or f16 and stand back a bit.

Stopping down the aperture will decrease the light, so you may need to slow down the shutter speed (use a tripod if it's too slow to hand hold, but don't go so low that your subject movement is blurred) and/or increase the ISO (test how high you want to go before noise becomes unacceptable). Or use flash (preferably off camera).

Is this a paid job? If so, why are you taking on paid jobs when your photography knowledge is limited?

Edit: Dunno what NickP is talking about - there's nothing wrong with shooting a portrait with a prime macro lens like the 60mm - it's a great focal length for portraits & if you want to (not in this shot) you could open it up to f2.8 for shallow dof. It is also far higher optical quality than the kit lens or any consumer zoom lens.

What happened here is that you didn't become a photographer before you started doing jobs.

To get them both clear, you need to stop down and get a larger DOF.

This answer might seem harsh, but the reality is that you are probably taking money, when you don't even have the basics of photography down.