Flags are shown on my own  buildings. In order to see how many units are actually garrisonned I have to directly select that building. If flags are not historically accurate there could possibly be a different visual indicator for the game's sake. For my own ships and siege engines, I have to select each of them to see what is actually on board, i.e. no flag or other visual indicator. For adversary buildings (and ships, siege engines) I have no information at all (which is ok as part of the game I believe).

Flags are anachronical in plenty of situations given the time period, but I wonder up to where historical accuracy is wanted. It’s interesting that one can see if fortifications are garrisoned, but not if ships are… which is usually the exact opposite of reality.

Hi friend! (Hola amigo) At first, this city wall most be added to the faction. (Primero, este diseño de murallas debe ser añadido a la facción) x Second, the houses. (segundo, este diseño de las casas) And lastly, I want to redesign the Civil Centre (Y por ultimo, quiero rediseñar el Centro Civico) Here some references fo the civic centre (Aquí algunas referencias que encontré para el centro civico) Quiero añadir esas puertas y muros techados, ¡la verdad me gustaron muchísimo!

Isn't that like in real life? Neutrality is not guaranteed , especially not if you harmed the other country. The AI consistently replying "not interested" seems strange to me. In SP, I often use neutrality which works in many cases (could not find out why or why not) and in a second step also an alliance which sometimes can be established. often there is a tribute to pay (1000 wood or the like) for one or the other.  

Good question! I just don't know . Similar to enemy towers, fortresses, garrisons etc. as well as siege engines. Own Buildings have a flag on top - select it to find out how many are garrisoned. Own siege engines don't have a flag and - like ships - you would have to select the unit in order to see if and how it is garrisoned.  For enemy structures this is always a surprise IIRC.