Being Disrespected in my own home

So I have a 2 and a half year old son and 8 month old daughter well my son currently sleeps with me while i sleep train my daughter as they share the same room. Well my sister and her boyfriend are staying with us as my sisters boyfriend is doing tattoos on me and my fiance. They decided to sleep on the floor in the kids bedroom which i was okay with Well i have my 8 month old sleeping in her crib and i have the baby monitor on and i woke up as i thought i had heard her start to wake up well i look and i see them having sex on the floor in the kids bedroom with my daughter in the same room. So i sent my sister a text to tell her i knew what was going on and she hasnt said anything to me since how would you handle this ?