Isga and Milan didn't expect Jason to be so confident about finding a branch of the exposed mana vein in a reclusive area at that.
While Milan was not sure where Jason got this confidence from, Isga began to wonder if Jason saw something through his mana eyes.
However, even if Jason was not sure where to go in order to find the place he was looking for, Milan knew the exact location based on the several maps he had studied, like the back of his hand.
As such both agreed to Jason's proposal before they set off, not minding what exactly was going on behind them.
Everyone was on their own and it was not their responsibility to take care of the descendants of the other families!
Milan tried to recall where they had to head to in order to find a place similar to what Jason described.
As such he was in his own world while following Jason, who knew where they had to go.