I don't know all the signs well enough to pin all the characters down to a specific sign, but I can say this.
SOLAS - Air sign. Probably Libra, lover of balance and justice, sees both sides of issue, rules with head not heart.
JOSEPHINE is also a very good candidate for this sign.
Those with planets in air signs use their minds to make sense of their lives. With Air, there's more space between the life lived and the observing mind. This can lead air signs to appear detached, aloof, remote, cool. Sometimes they'll try to talk their way through feelings or analyze a situation instead of encountering its full emotional weight.
Since Libra is the Cardinal air sign, it is the leader, the Way Shower, the instigator. Thus Solas shows the way through new ideas, and being a balancing force (between "good" and "evil").
BULL - Earth Sign And yes, I think Taurus. He has a philosophy strongly rooted in the pragmatic, practical and here and now. IF HE HAD A MOTTO, IT WOULD BE "IT IS AS IT IS."
Taurus enjoys the sensual world for it's own sake (compare Virgo which has to do something with it). Down to earth, pragmatic, will stubbornly pursue a task to completion without deviation once it has the impetus to get going (which may take a while).
Pitfalls
Taurus has difficulty seeing beyond the end of its nose. Philosophy? The spiritual realm? Forget it! The earth is all there is and I'm going to enjoy it. So limited resources when the earth disappoints.
I'm not sure about the rest.