They are test tube babies designed by a sentient virus, I think nearly anything is possible. They may only have 10-25% DNA from the male donor, anything from them might be supressed by design until the phlebotinum is applied, real world limitations don't need to apply in comics.
Their body posture suggests the one on the left is superego Sophie and the one on the right is id Phoebe.
"We come into this world alone and we leave the same way. The time we spent in between - time spent alive, sharing, learning together... is all that makes life worth living." - Jean Grey
Btw shouldn´t their family name be Frost? Emma is her only known parent so IMHO it makes sense they wear her family name.. Esme Frost, Sophie Frost, Phoebe Frost, Mindee Frost, Celeste Frost)
Primum vivere deindre philosophare
Well actually a story where they end up claiming the Frost name would make sense and would be interesting to read
Primum vivere deindre philosophare