The Eternals are like the X-Men. There are many of them and so not every story has to focus on the entire group. A movie with just the group who ended up in space would be fine by me--although at this moment I can't even remember who was in that group.
If you mean the ones that left on the spaceship, it was Thena, Makkari, and Druig, according to the Wiki. I can't support any plan for an Eternals sequel that doesn't have Gemma Chan in it.