Let me take a crack at this, to my understanding this login wallpaper was supposed to be live during a festival, but was delayed for some reason? Almost all the dolls here are Italian, so that should narrow things down.
- The Carcano sisters
- Z-62 and BM59
- Astra Revolver
- M12 (although her ponytail is a bit longer then what it is in her base CG)
- G41 and 9A-91? being the odds ones out.
I'm also pretty sure none of these are costumes from a procurement pool either. At least not yet, who knows, maybe the devs might actually implement them in the future, but right now I dont think they exist in-game. (Someone on the JP server could correct me on this)

Here's my thoughts on who these characters are (from left to right):
- Most likely M12, but could possibly be Type 64
- Definitely G41
- Likely AS Val over Z-62 (Z-62 has circular glasses and paler hair)
- Probably BM59
- Carcano m1891
- Probably MG3, since her appearing is very similar to her Halloween outfit (minus the animal ears). Could also be KSVK
- Either Astra or EVO3
- Carcano m91/38

Far left is M12, though her neckerchief and shorts are a different colour. Type 64 is generally seen with a braid rather than a ponytail, but the most telling is that M12 has blunt bangs while Type 64's are sharp.

Whatever the context, I find this art pleasant. I'm kind of hoping the coming login event for EN will have this as an ID card or something like that.