No this is not normal behavior. I know you mentioned that you have children of your own, please be proactive and
But this actually isn't his DD--it's his stepD from his previous marriage. I think if it was his DD people wouldn't be as suspicious (I know I wouldn't anyway).
I do remember when I got divorced, my kids would spend every other weekend w/ their dad. One time, my DD wanted to bring a friend over for the weekend. I think they were in middle school age at the time. The girl's mom called me to kind of feel things out and I was kind of insulted because I felt like "gee, do you really think my ex is a child abuser?" She did actually know him because he would come to our girls' soccer games, so he wasn't a stranger. But she did feel better when I explained that he was living w/ his GF so there would be a woman in the house too. So I agree w/ the previous poster that a guy taking 2 teenage girls & staying in a hotel really isn't a very smart idea.