with a young horse with a known injury ( the kick) I would go aggressive.
As a vet told me once, do it the right way, now , or pay for it in the long term.
if the owners are having you train to reach some show or sale goal, if the horse is off at that time, they lose.
the horse will not forget its training. In fact a young horse like this ( started as a 2yo?) could likely benefit from a month or two off.
we had a long thread here, recently , about one of our members struggling with teaching a young student on a notably off horses. The parent owners had to be compelled to get diagnostics.
The owners say they will not blame you if things go wrong, but I suspect you will blame yourself. I bet many of us , in the same situation, would feel guilt and sadness that we did not do more
Perhaps you have to take a stand as a professional that you cannot , in good conscious, continue to push this young horse into more severe disability