If you live with them and are very close, it might be impossible to keep the secret. And you might not want to do that, as they might help a lot when the morning sickness and fatigue sets in.
But you need to be aware that, in case the worst happens, they might not be able to be supportive and might make thinks a lot worse despite their best intentions. I regretted telling my parents, my in-laws and closest friends soo much when i had the miscarriage at 10 weeks. It is impossible for someone who did not go through that to understand and help you. My experience with telling people early ended in the worst way, all because they tried to help....and they hurt me more than i could bare. I really hope that doesn't happen to you.
Sorry for all those crazy characters where apostrophes should be!
We told our parents and my husband's brothers and their wives right away. We're very close to our families, and we wanted them to be able to celebrate with us. Also, if something did go wrong, we knew that (a) they would end up finding out anyway and (b) we would want them to be there for support. The point of waiting is so that if there ends up being a miscarriage, not everyone has to know. However, it sounds like your parents and in-laws would know anyway, so you might as well tell them! But you can tell them that you aren't ready to share the news with anyone else yet.