I felt the same, and even that if both were girls it would be different (if both were boys it would not be, because any DIL would be expected to take the role on), because a daughter would potentially have been expected to behave differently. Not necessarily supported in obtaining diagnosis and treatment, but at least required to behave like a good daughter around the house and develop domestic skills . The gendered aspect has harmed both, and neither LW nor her brother have been served by this.

Anyway, LW needs to grasp that if her brother moves in her marriage is doomed in the long run, and not ruin her own life.