Traveling with a toddler, staying with the whole fam damily?

My husband and I are planning to attend his brother's wedding in October. We will be traveling by car with our 18 month old daughter. It's a 6 hour drive that, with a toddler, will take literally all day. Not fun. The real humdinger is that we will be staying at his parents' house... with 13 other relatives. In a 4 bedroom house. The problem is not my in-laws. They're great people and we get along wonderfully. The problem is that there is not enough space to house 16 people, two of which are toddlers. My daughter will not sleep in a room with anyone else. She simply will not. I've tried. Secondly, there are stairs at their house. My daughter has never encountered stairs before. I am so afraid that she'll get hurt on them. Thirdly, I KNOW I won't be able to sleep with other people in a bedroom with us. I have a difficult enough time sleeping through my husband snoring, flip-flopping, etc. So my question is this: Do I disappoint my husband's entire family by not attending and also keeping my daughter here at home with me? (She is the flower girl for the wedding.) Or do I ask my doctor about sedatives and tranquilizers to help me "put on my big girl panties" and deal with a less-than-ideal situation. I'm already having panic attacks and the wedding is 2 months away. Yes, I am a high-strung worry-wart. I've been working on this character flaw all of my adult life. Any reasonable suggestions will be highly appreciated. Anyone who tells me that I'm over-reacting, I already know that I probably am. But if there happens to be anyone out there who happens to have been through a situation like this before, what did you do?