Good morning!
1. As far as I know there is no download resource for the DoW-Mod. Its usually provided by request.
2. As a superior commander you can take over the direct control over a formation or unit by clicking on the flag icon upper left corner of the toolbar. This meassurement gets executed as soon as the corresponding courier reaches the addressee. Then the flag icon gets highlighted and the AI is excluded from its control. In that case every disposition has to be done by the player including changing the formation like square if enemy cavalry comes close.
If you set a most passive role for a brigade by setting its commanders stance to "hold to the last", the brigade´s initiative is mostly off, but its single bataillons still keep a certain reactivity when enemy formations get into its immediate vicinity.
3. The basic doctrine of napolenonic battle formations intends to ideally have for every front bataillon a reserve bataillon backwards to relieve the fighting formation if it has to fall back or withdraw due exhaustion, moral issues or lack of ammo. Thats probably why the AI keeps a fresh bataillon in passivity. Its a very important principle, because if a line breaks and enemy units cut through, they were able to flank other already involved fighting bataillons, which often has the potenzial to let collapse the whole formation.
In the current situation according your screenshot a passing to the left shouldnt be an option because of the building, which probably had the effect of an obstacle and at least rather would interfere the unit´s efficiency.
If you really want to relinquish the provided reserves, you could also try to set the AI commanders stance on a more agressive level, so it might be possible that reserve bataillons get involved sooner. But it is also a fact that often the AI doesnt outflank firendly units properly, but theres a certain overlapping, so the backwarded parts of an overlapped bataillon are blocked from firing.
We have to accept that a perfect lineup just cannot kept up in the heat of a battle. Sooner or later napolenonic warfare becomes a chaos and its the task of a good commander to try to minimize this chaos without causing an even bigger mess.