If Magda is Natalya and came from a family strong in magic according to Marvel it makes sense Chthon would find her offspring suitable to get into the real world, if we forget the Axis retcon and add Magneto´s own bloodline that came from science then you have truly unique descendants that have a mixed origin for their power, one natural and one supernatural. There was even an old marvel comic that talked about Chthon being interested in Magda´s twins because of this strange mix of Science and Magic, if you ask Dr Doom that makes for a powerful mix. If we follow Wanda´s series it´s possible Natalya(magda) died confronting Chthon and the HE for her twins.
I hd Chthon also has had a lot of influence over the twins lives and that´s why their life has been so caothic and why they sometimes go over the edge mentally and emotionally apart from their own troubled origins of course.