Ok so what i gathered from the chapter is…

1- Mindless titans who eat a shifter, become able to turn back into human form and turn back into a titan thus, becoming a shifter thenselves.

2- Grisha was a shifter, he gave Eren a serun wich turned Eren into a mindless titan, and allowed himself to be eaten by him so Eren would gain his powers.

3- Grisha killed the Reiss family, while they were underground inside a small chapel. The reason for that seems to be to gain the coordination ability from one of the family members.

4- Eren seems capable of remenbering stuff about his father. so either that has to do with shifter herintage, or that's a coordinator's special case. Wich also explains why Eren saw through the eyes of one of Reiss's family members, specifically the eldest daughter, who we called "Geographia" for fun, so she was most likely the coordinator.

Also, saw someone speculate on something because of this chapter and it seriously makes sense… The titans are only eating humans, in order to become humans again thenselves, they don't need to eat, so the eating is done in the hopes of finding a shifter and turning human again.

Eren ate his dad…