Now, if we look at their original appearances:
Marie Von Helson -

Anna Corinne Von Helson -

Perfectly normal, in fact one could almost say flawless - which would support a Vampire heritage, since accelerated healing is a Vampiric trait.
Now, two years later - lets have a look at their appearances:
Both Twins -

The first noticible thing is their shredded clothes - understandable, two years of no money and recovering from serious injuries: but WHERE!
There are only two Doctors on Gaia who we know about - the Doc that fixes the Robot (see Mini Comic 25th June) and Dr.123 - aka Labtech 123. The very same Labtech that X somehow got the virus from when he started making it again.
They also have much paler skin - a trait shown by Zombies.
Are we, with the re-apperance of the Sisters, seeing test subjects of a new strain?
Because, if you notice Marie has heavy stitches across her face and waist / hip - if they were pure Vampire, the healing would have been much faster, and their would be no scarring.
So, assuming that the Von Helsons are Vampires, it seems likely that Marie has some human DNA mixed in - making her and her Sister halfbreads, that MAY have been subjected to the G-Virus.
This would make them Vampire/Zombie hybrids - with more than just a lust for blood.
Which would mean a brand new virus - perhaps the product of the mysterious box Labtech X was seen giving to them before Gambino's tower fell.