I never got anything incestuous between the twins, mostly because of Wanda's interest in Cap. Just two orphans who'd had to rely upon each other to the extent that Pietro's overprotectiveness prevented Wanda from any healthy human relationship to the point of hooking up with the Vision, and leaving Pietro no time to pursue what might have been his own interests. I always read Pietro as gay, and the Crystal thing seemed imposed purely to get him out of the Avengers and free up Johnny over in FF. There seemed so many parallels between the gay and overprotective Northstar and his twisted sister, Aurora, that I'd always wondered whether he's had the Maximoffs in mind when he fleshed out the Beaubiers.