It's tough, but you're doing an alright job at it. I feel learning the skull and the planes of the head help a ton, getting different viewpoints from various artists also helps to further your understanding of what's important
Proportions look alright overall, where I feel you may be having more difficulty is in the 3D form of the head and its features. When in doubt, try making contour lines either horizontally or vertically. For example, a vertical contour of the midline when you compare to a profile view can help you see if your features are in the right perspective, and horizontal ones help a lot with things like the eyes. It happens all too often, we focus on getting the details well drawn but don't realize that we have two or three perspectives in one portrait
As an example, on the last head, try drawing entirely the ellipse of the brow line through the skull sphere, note the eyes are kind of on a horizontal rather than wrapping around the sphere and placed accordingly, the lids have no thickness/overlap and the nose is facing us while showing a side plane at the same time
There's nothing wrong with re-iterating the same face and angle or erasing/fixing the same one to further enforce what you're learning. I struggled a lot at first and I still feel I need to learn a lot more before my heads are any good from imagination X_X
cheers!