For RotS, it’s a mess. There’s individual novels. The closest to a “series” I can think of would be The Proving Grounds trilogy involved the Northwind Highlanders (now a Republic unit). Fair warning, these were early DA books, so the numbers of mechs are bizarrely low as the setting has sort of backed off the scale of disarmament over time.
A Silence in the Heavens
Truth and Shadows
Service for the Dead
Then the Highlander Covenant duology
Grey Watch Protocol
Paid in Blood
Otherwise, it’s individual novels. But there’s no novels covering the formation or really anything until just before the blackout.
For FCCW, maybe go Archer Chritifori novels. Measure of a Hero, Call of Duty, Operation Audacity.
While not a series, Illusions of Victory is good and seems to take the piss out of Solaris while writing a love letter to Solaris.