There is a lot of myths and rumors about sampling someone else's music for your own, but I don't know what is true and I'd rather not take any chances. Again, I am sampling for non-profit, and I am a completely independent producer.
Patent Application Attorney
Non-profit and independent status have no role in liability for copyright infringement. Sampling has always been very controversial. See the movie Copyright Criminals for a discussion on the subject.
Intellectual Property Law Attorney
If you want to know for sure, as you say you do, hire a copyright attorney, preferably a music industry attorney. Independence is not a defense and working for a non profit is not a defense. This does not appear to be fair use. You will likely need licenses if you want to be safe and legal.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
Unless there is something unusual in your particular situation which is not disclosed in your question, you will need a license from the owner of the sampled recording, plus a license from the publisher of the sampled composition. There is a fairly standard protocol for obtaining such licenses. Expect to pay an initial advance for both licenses. Good luck.
The above is not intended as legal advice and does not constitute the creation of an attorney-client relationship, as this forum does not provide for a confidential communication. Furthermore, the attorney's answer above is intended to be general information only, and there may be facts not contained in the question which could change the answer, so the answer above should not be relied upon without first obtaining legal advice from your own attorney.