The most important thing to establish right now is exactly where the case stands in the legal process, because that determines what options are actually available.
If he has not yet entered a plea and the case has not gone to trial, he is entitled to a public defender at no cost if he cannot afford private counsel. What most people do not know is that the right to counsel also includes the right to an investigator paid for by the state or federal government. That investigator can gather evidence, interview witnesses, and build the factual foundation for a defense. If you have information that supports his innocence, getting it to that investigator is one of the most concrete things you can do right now regardless of your financial situation.
If he has already entered a plea or been convicted, the options narrow but do not disappear entirely. Post-conviction relief, appeals, and in some cases innocence projects that take on wrongful conviction cases without charge are all avenues worth exploring depending on the circumstances.
On the broader frustration about sentencing disparity, it is real and well documented. Drug charges in the federal system in particular carry mandatory minimums that produce sentences longer than many violent offenses. That reality is what makes having skilled legal representation from the earliest possible stage so critical. Plea deals, sentencing arguments, and cooperation agreements all happen before trial and shape outcomes dramatically.
What you can do practically is document everything you know, write it down in detail with dates, names, and specifics, and get that information to whoever is handling his defense. Your knowledge of the setup, if it is credible and specific, is exactly what an investigator needs to work with.