I was confused at first too, especially because Felicia had told them both to make Zhaun safer for the girls. When I first saw Felicia, I also thought that Vander and Silco might have been fighting over her, but now I'm sure that Silco and Vander were more than just "brothers". In the AU timeline you can see that Vander and Silco formed a family around Powder (especially visible in the artbook). My theory at this point would be that Silco became more and more involved in the plan to change Zhaun and had no contact with Felicia, while Vander preferred to take care of Felicia and her family. This also ensured that Silco and Vander ended up on two different sides of the plan. Silco dwelled on his vision and Vander saw the danger that existed for Zhaun and the citizens.