According to the source, the character on the right is Shiro. I don’t see a tag for her, so should it be Shiro-chan, like most of his other characters? I’m giving her a preliminary tag, but I’d appreciate someone confirming/refuting it. (I tend to see her referred to as imouto-Shiro too.)

Yoru’s only other artwork describes her with chan (tsun-tsun succubus-chan), so I’ll give her a preliminary tag as Yoru-chan too.

The maid is still unnamed. Mignon’s referred to her as Maid-chan, so I’ll use that as a placeholder tag for now.

Update: Her name is セイラ. With a literal romanization, it would go to Seira, but Mignon chose the name Sarah. He also refers to her with a san. I’ll likely update the tag later today.