Well, for some reason I don't think I ever ran across this thread, but I cannot see any of the maps, as the links appear to be dead
When JJR and I worked on the tech bible for the 14th Colony (14/CTB), our assumption was a single, trinary system, with several Colony worlds being moons of gas giants ('GG').
As to the radiation questions, in RL it is true that inside a certain distance, GG radiation is lethal to Humans - however, outside the band, lethal radiation falls off precipitously, leaving aside the issue of GG-moon Van Allen belts.
Although I don't believe we ever speculated on how there came to be 12 habitable planets in the 14/CTB, I have speculated elsewhere (have to find that link) on the existance of a "prep team" that went ahead and "fixed" (i.e., "terraformed") the rest of the 12 Colonies' worlds...
