So I rewatched the last trailer, and there is a shot of one of the Viltrumites getting hit, with a pink background behind him. Almost all other shots were from episodes 1-2, so it’s fair to assume only parts of part 1 were used in this trailer.
So considering Nolan is one of the most popular characters, considering that this season will feature the VA for battle beast, and considering part 1 needs to end on a cliffhanger to keep hype alive for part 2, I am guessing that episode 4 will have the big brawl in space.
We know for a fact that Thraxa will be Episode 4 because of the episode titles. However, there are so many points where they could end on a cliffhanger. Mark meeting Nolan, Mark meeting Oliver, Nolan revealing to Mark that the Viltrumites are on their way, or Kregg assigning Earth to Mark. The battle being in the trailer isn’t enough since we also see flashes of the Guardians vs the Lizard League, which is definitely Part 2 material.