It's kind of silly you saying that for "20 years before the twins had no familial relationship with Magneto", no, but they were more involved with Magneto than Whizzer and Miss America considering the first time we saw them they were in the Brotherhood. And what arcs did they have before Mags? Marvel was always putting Wanda in peril or having her lament over Vision. The family connection made everyone more complex, it's a foundational character trait.