Gram is either Austin Tindle (Ayumu Aikawa, Marco Bott) or Lucien Dodge (Waver Velvet, Blue from Pokemon Origins). I imagine more on the Austin Tindle side, though. He has the voice for the yangire vibe I'm going for.

I [i]definitely[/i] imagine Brittney Karbowski (Yuri Nakamura, Ikaros, Mikoto Misaka) being Atalanta's voice.

If we're going Japanese...

Gram is voiced by Megumi Ogata (Makoto Naegi, Nagito Komaeda, Shinji Ikari). Most fitting voice ever.

Unfortunately, my knowledge of non-male-acting female seiyuus is rather low in comparison to my knowledge on their male counterparts. So I'm at a loss about Atalanta's.