Mike and Mitchell Durkee made their initial appearance in Marathon County Court Wednesday.
Mike faces six counts of second-degree sexual assault, and Mitch faces six counts.
The criminal complaint says the brothers had sex with a 15-year-old girl at different times in a trailer at the Wildlife Campground in the town of Norrie.
The alleged assaults occurred just hours before Deanna Zulegar Scantlin was kidnapped from the bar at the campground.
Mike Durkee is also accused of having sex with the victim five more times. The girl is now pregnant.
The Marathon County Sheriff's Department says the fact the alleged incidents occurred the same night is just coincidence, and Dale Robinson is still the prime suspect in Deanna's disappearance.
District Attorney Jill Falstad says this will have an impact on the prosecution of Dale Robinson, but she doesn't know how.
Each charge of second-degree sexual assault carries a possible 30-year sentence.