Necropolis – “Forward and Inward” [Campaign 2, Mission 2]

By the way, for some reason, after reaching level 2 in the Blood path, the Tears path didn't unlock... even though I reached level 1 in the Tears path... but it still didn't activate... Why? Does anyone know?

According to the achievement descriptions in the Dynasty menu, switching from the Blood (Tears) path to the opposite path is possible and even recommended for the sake of 2 achievements. The nuance seems to be that the switch is possible only after reaching the first level of the corresponding path. For the achievement, you should accumulate 250 points (level 1 of the opposite path) and then continue developing the main path (up to level 2). And do this twice (first from Tears to Blood and then from Blood to Tears) :)
There is another way - take a hero with the first level of Tears/Blood maxed out and max out the opposite path.