Even though I don't have him, Force (Force Fox by FallinDoll) would sound either like a male version of Raven from Teen Titans/Teen Titans GO or like a male version of Wednesday Addams. Then his singing voice (since he's an aspiring rockstar) would either be that of the lead singer in the band Fall Out Boy or maybe Freddie Mercury (not sure).
Syr was heavily inspired by Motoko Kusanagi from the anime Ghost in the Shell: Stand Alone Complex, and her voice in my head is basically Motoko's voice. The voice actor is Atsuko Tanaka, who also voiced Motoko in the two GITS feature movies directed by Oshii. I work at a secondary school, and Vallant and Justinian sound like composites of all the senior teenage boys I hear around school. Gael is a singer. His speaking voice is baritone, deeper than Vallant and Justinian. As for his singing voice... my friend was filming a Catholic mass in a cathedral in Spain. There was this baritone soloist singing the mass, and when I watched my friend's videos I immediately went "THAT is exactly Gael's singing voice." Wish I could share the videos.