House Guest During Fertile Week!

I have been trying to get pregnant for six months. I would love to be pregnant any month, but I really want to get my bfp this month so I can surprise our families for Christmas. Unfortunately, this week is my fertile week and my mother in law is staying with us! Our apartment is really small so there's no way we can just be quiet. It's hard enough to schedule sex each month during the fertile week, but now we only have one half hour window where we are both home and she isn't. Advice???