Stephen's sisters only appear briefly in the novel. Half of the point is that there are a lot of them. Before Episode 10, it seems as if all of Stephen's remorse is focused upon something that he cannot control: the fact that he did not pray over his mother before she died.
When the sisters are introduced in "The Wandering Rocks," it becomes very clear that Stephen's independence is coming at a price for his sisters who are subject to their drunken spendthrift father. Stephen thinks that Dilly has a glimmer of his own intelligence, but cannot bring himself to help them for fear of ending up in the same situation.