I didn't even notice that their hair was the same. But if that is true, than Hel would be Alfonse and Sharena's alternate mother, in which case, Eir doesn't belong. This furthers my theory on Eir being dead Sharena
She couldn't be their mother since, if I recall correctly, Sharena mentions that she and her mother send each other letters due to the fact they don't get the chance to see each other often with all this Embla business