Actually, you should not have to worry about the orientation of the faces if you set up the setup as follows:

Instead of changing the points of the geometry here, I change the whole instance instead, which basically preserves the normals.

However, to accurately answer your question regarding the normals of the faces, it would be helpful if you share your blend file.

_{(Blender 3.2+)}

Actually, you should not have to worry about the orientation of the faces if you set up the setup as follows:

Instead of changing the points of the geometry here, I change the whole instance instead, which basically preserves the normals.

However, if you then use the node Realize Instances, the normals are flipped for some objects.

To avoid this problem, create a boolean value on the instance beforehand, which makes it clear that this instance should be flipped.

In this example I create this value via the Dot Product.

_{(Blender 3.2+)}