Are they supposed to take fuel from the depots they can access, asking because it feels like they should, but for some reason they are not taking fuel from the depot

Yes they should take fuel from the depot, but only if there is at least a full stack available.

I find they accept some fuels from depots and not others. For example wood grown in the greenhouse can be manually placed in the structures as fuel but it will not be automatically removed from the depot, unlike coal.

I currently have very little free time to work on this mod, but I will look into this further.

I'm unable to have the structures even accept coal, no matter how much is in the depot.

EDIT: please ignore, I think it took a second to update, or maybe I placed the depot too far away?