I still haven't found a page that names which members of the BB sound team are a part of Metasequoia (although it's possible all of them are), but I wanted to at least jot down who I believe is in the current photo we have.
The one on the back Keyboard is Naoto Oike. Compare him with our image of Oike and he just has less hair all around. He also shares an instrument.
The one on Bass looks pretty similiar to Junpei Mishima, but it might not be him. I know Mishima plays several instruments like Bassoon and Ocarina, but I don't know if he plays Bass. (assuming it even is Bass. I don't know the visual difference between an Electric Guitar and an Electric Bass Guitar)
The other two are wild guesses, as I believe them to be Kazuki Takagi and Yasuyuki Nagata, based on the idea that neither look like Fumio Ito and they're obviously not Megumi Takano. Which is which? The only thing I can think of is that some of Nagata's tracks use very real sounding Guitars even after Tomoya Koga left the team, so it could be Takagi on Keyboard and Nagata on Guitar.
EDIT: Since Tomoya Koga was credited for guitars on the Metasequoia songs from BORDER BREAK MUSIC COLLECTION TYPE-02, that's probably him.
EDIT 2:
Picture of Seiichi Hamada as a member of Metasequoia.