16 - 23 million is not much money considering a 300 million dollar box office gross, especially if divided by the four Tuohy family members. Oher had a nine season NFL career which included a Superbowl win with Baltimore. I have no knowledge or recollection of him doing endorsement deals.
The substance of his legal action lies on whether the Tuohy's influenced him (as a minor) to surrender rights to his story. If they did, then they failed to act in his best interest as conservators and effectively cut him out of something to which he had an inherent right - his life story.
There's a lot that we'll never know like how Mike's would have turned out without the Tuohys. We will never know if another party of influence might have stepped forward to see Mike's athletic potential realized. We'll learn a lot about the parties as the case evolves. I suspect none will be nominated for sainthood when all is said and done.