They don't necessarily need to have the actual drugs -- witness statements and statements on phone calls can be enough to prove weight issues. You can call if you have further questions on your situation.
In addition , you can look for sentencing de idioms of a particular judge in the press releases found on your local US Attorney's website. It is a bit tedious, but can be done. You can also get an account on the PACER website, which is where you can find any document filed in any district, including sentencing judgments. Finally, you can always do Google searches of the judge for articles, etc.
You should definitely look for a federal lawyer, someone familiar with the prosecutor's office in your area. It would also be helpful if that person has experience with US Fish & Wildlife investigations.
The safety valve allows the judge to sentence below the mandatory minimum, but the 5K1.1 alone does not -- that only allows the judge to depart downward, as far as the mandatory minimum, in your case 5 years. 18 USC 3553e is basically the statutory equivalent of the sentencing guidelines' 5K1.1, but it has the additional advantage of permitting the judge to go below the statutory mandatory minimum as well as to depart downward generally. So, in negotiations, it is important for the attorney...
More information is needed to give you a more complete answer, but I would strongly urge you to contact the attorney that represented your sister at the sentencing phase of her case. That person should be able to explain the judge's reasoning for the sentence. My assumption is that the sentence included a conviction or convictions for gun charges under 18 U.S.C. 924(c), which can carry enormous sentences, that must be served consecutively to any sentence imposed for the underlying offense....
In addition to assessing Mr. Richman's very helpful answer, my advice is that you schedule a time to meet with your lawyer to discuss your situation in detail with him or her. Your lawyer is in the best position to assess the strengths and weaknesses of your case and to calculate the guideline ranges you face if you go to trial and lose or if you accept a plea agreement and plead guilty. Best of luck.
Not necessarily, but he could be. He is at least a potential witness. The government may also to add him to the charges (through what's called a superseding indictment) at a later date. He should definitely contact a federal criminal defense lawyer and seek that person's advice and counsel.