Age of Empires II Definitive Edition Guide

Build a Monastery or Shrine in every Lithuanian village in "Family Affairs".
This achievement triggers at the end of the mission, so make sure you've done it before you complete the main objectives.
It also requires that you advance to the Castle Age.
Once in the Castle age, you can construct Monasteries or Shrines to convert 6 local villages to your cause (Grey).
If you build a Monastery in a village, then the village begins periodically giving you gold.
If you build a Shrine, then they aid you by sending troops at your enemies.
You can pick any combination of Shrines and Monasteries in each village as long as all six of them have one or the other in.
If you choose to build a Shrine, they will assist with Battering Rams as well as infantry, so they can be a little useful.
On the other hand, neither your ally (Teal) or any of the villages have a Market, so you are unable to trade meaning if you choose to build a Monastery, you can get a steady flow of gold.
Monasteries produce Monks and Shrines produce priests which have the old school Age of Empires Priest skin, however their stats are the same - As are the stats of a Monastery in comparison to a Shrine.