If your husband likes to keep guests at a minimal, then that is his (or your) right. Just tell them the truth, "I'm sorry, my husband is not comfortable with 2 people sleeping over. He feels it's too crowded."
Are you afraid they will be having sex? Highly unlikely, speaking as someone who has slept (with my husband) on couches and guest rooms of family/friends over the years.
Are you afraid their chatter/bumping into furniture will wake the baby? That is a valid concern. Share that with them.
My husband, young son & I used to sleep in my SIL's guestroom attic. She has a special needs son. She eventually told us we couldn't stay there anymore because our presence was a distraction to our nephew's nighttime routine. Bummer, but we love her, him, her family and we were not offended or insulted. We get it. So SOME people will take offense (too bad) and others won't. You know your friend best.
So have an honest talk with your husband and see if he can deal with it or not. Is it worth it if your friend is put off? Then again, having a COMPLETE stranger in your house is no easy matter either. I had a friend once bring her boyfriend and our cat pooped on his pillow. He never acted like that with anyone. So our cat was freaked out by this person.