I knew about the Maximoffs, but where did Lorna Dane come from?
Well, she has the same powerset as Magneto (iirc she went by "Magnetrix" for a bit before the current "Polaris") so it was a suspiscion for a while, but I think it got confirmed in X-Factor (possibly around the same time Theresa became the Morrigan?).

Basically her mom had an affair with Magneto, her mom and step-dad died, and Lorna was raised by her step-dad's sister and brother-in-law.