In order of appearance: (click on the thumbnail for a larger picture)
Alison
The leader of Orphan. Friendly and forthcoming, she often helps out the less fortunate children in New York - not necessarily through legal means. As Akagawa mentions, her relationship with Yuki is almost that of real siblings. She is also close to many of the adult members of Orphan.
[spoilers]
Is killed by Akagawa in the July '03 instalment.
Akagawa
Polite without being overly formal, he too has an almost brotherly affection for Yuki. His weapon seems to be the Chinese kau sin ke or whipping chain, which he uses to devastatingly efficient effect, but he's also quite handy with a gun.
[spoilers]
In the June '03 instalment, Akagawa's cool demeanour gives way, and we see that he has a disturbing obsession with Alison that may prove dangerous...as it eventually does. He is killed by Aya in the July '03 instalment, at Yuki's request.
Yuki ( see also Krypton Brand Side B )
Apparently the youngest active member of the group, Yuki seems to be still unsure of himself and his abilities. The fact that some Orphan members call him "gaki" doesn't help very much, either. Note also the current lack of spectacles. ^_^;;
[spoilers]
In the June '03 instalment, he receives a wound to the eyes, which may go some way to explaining why he wears spectacles in the main timeline.
Doctor D
Apparently the resident medic in Orphan, and familiar to the kids as well, even if he tends to be good-naturedly patronising. Appears rather eccentric, but can be efficient and focused when the situation calls for it.
All members of Orphan. Hyuu is killed in the Blue Eyes' attack on Orphan in the May '03 instalment. Chris is held ransom, but later killed when Orphan attempt to rescue him. Doug and Marty are killed in said rescue mission. Pictures can be found under their corresponding instalments.