the factions choose the surrender terms and if a tyrannical faction is trying to impose impossible amounts then the two faction might not agree on the surrender agreement but if a surrender agreement is reached with impossible resource amounts then the tyrannical faction simple will only get the resources which the defeated faction can provide
a faction can then split the resource amount between each player using the mission system so each faction member has to provide his equal share
and the faction can do what it wants to faction members not pulling there weight
yes you will be able to steal resources from other faction land but if you get caught then...
and to protect you faction resources walls and fences are a good idea or guard patrols and watch towers