So, as someone who's up to date on Twilight Axis, here's some information I can share with you.

So far, no direct links to Unicorn- but a very strong link to CCA.
Basic story is this: Ex-Zeon engineers living new lives are forced via blackmail to assist a Federation (?) squad of Special Forces to investigate the remains of Axis and recover the Sazabi.
*Upon entering, the team are attacked by a team of new Jegan models and the Gundam Tristan.
*Our protaganists escape into an underground hangar and find a Zaku lll that was customized, but never used for Char's use by his wife.
*Using the Zaku lll, they manage to drive off the Tristan. Later, the team go deeper into Axis. A new, space combat Byarlant is discovered, and the protags jump into an R-Jarja (!) to fight it off.

There is a direct link to Unicorn. Character asks another what he knows of the Laplace incident and then mentions the Unicorn Gundam.

The Ronah family make an appearance discussing the contruction of the Frontier colony. Twilight Axis is a prequel to F91