One of the deleted scenes shows the siblings talking about an experience they had a while back where Trish took the fall for one of Darry's mistakes.
According to info given about the next films, Trish ends up having a son years later, whom she named after Darry.
The sequel has Double D. and Izzy going to help Scotty, the racist & homophobic Jerk Jock who ends up pinned to a tree by the Creeper's knife. So, aside from his girlfriend, the only other 2 who care to help him were the ones he was prejudice toward -D, the black character and Izzy, whom Salva calls his gay character. Even more symptomatic of Double D because Scotty actually wanted to throw him off of the bus earlier, and D. swore then that he would not help Soctty if the Creeper were to get him.