Soo... Earth is a pure Vasudan colony that is then attacked by UIMS?
Did you actually replace ships in mission 1 or did you add even more? I couldn't play that mission because it crashed, probably because there was too much stuff to load.
Earth isn't a pure Vasudan colony. Earth is the homeworld of humanity/Terrans.
The Vasudans happen to be here and has been surveying the planet ever since their arrival. They appear to be witnessing events, the same events that happen in the 2018 Mortal Engines film, which sadly bombed so badly. Until the UIMS attacked. They witness the destruction of Airhaven, the attack on the Shield Wall and the annihilation of most of the airship fleet, and the air raid. Later, in the ensuing attack, the Jenny Haniver was shot down by Vasudan forces while trying to fend off UIMS fighters, and Tom and Hester aboard are killed. Humanity is wiped out to the last individual, and the Earth is ground to dust. It is one of the events that, along with the Battura, may have caused the Shivans to appear.
For Mission 1, I replace ships. It may be caused by a number of ships, but it may be something to do with your outdated graphics card and drivers.
As for the Battura being flat out stolen from Star Ixiom, they are merely temporary models, and that they WILL be replaced by high-poly ones.
This is the case for Bosconians and Sadeen. And the UIMS (save for Cylon-based ones).