Am I allowed to use other peoples instruments in my music?

Yes. Instruments are not protected under copyright law. They're too simple.

He said instruments, not melody or something that is protected.

This seems not to be actually about taking a tiny amount of music from a music recording, but about getting a sample of a music instrument. There are people recording say individual trumpet notes, likely in various degrees of loudness, and creating an "instrument" that can be used by a synthesizer so a keyboard player can create something that sounds remarkably like a trumpet.

If I create a record and want some trumpet music on it but not hire a trumpet player, I can pay for such an artificial "trumpet". I pay a license fee, and that will give me the right to use this recording in my own music. The creator of the (digital) instrument has the copyright. My music recording is a derived work (with plenty of my own copyrighted components obviously), but with a proper license, so I am fine.

The OP isn't actually interested in a copy of my music. He wants to get the notes from the "trumpet" instrument. That's what he expressly said at the beginning of the post. Extracting the instrument will be copyright infringement, and it will be most definitely not "fair use" or "de minimis" because what he is doing is directly destroying the livelihood of the instrument creator.

I can fill out with more detail later, but the Sixth Circuit held in Bridgeport Music, Inc. v. Dimension Films, 410 F.3d 792 (6th Cir. 2005) that basically any sampling of a sound recording, no matter how short, is an infringing use.

Despite that, you may still be able to establish a fair use defense, but that's going to be very fact-specific.

Your question is whether you can copy instrumental portions of recorded music, and modify it to create a new work, without permission. The answer is that this is illegal. This would be creating a "derivative work", and under copyright law, only the copyright holder has the right to authorize creation of a derivative work. Whether or not you have paid for a copy of a recording, you would still need a separate license to legally extract and use part of a recording. This includes taking just one instrument, and includes taking just a part of one instrument. Material on Youtube is subject to different licenses: in some cases items are free of restrictions, in some cases, you can't legally copy them at all. The standard Youtube license does not allow any copying.

Copyright infringement of music is rather common. Enforcement of copyright must be pursued by the copyright holder, and you would need to discuss your specific plans with a copyright attorney to determine your probability of getting sued. Ultimately, you might get away with minimal copying, relying on a fair use defense (you still get sued, but you might prevail and not have to pay). There are street rumors that there is an N-note threshold for copyright infringement, where people often pick numbers from 3 to 7, but in fact there is no clear rule. This resource assembles relevant case law.

Bridgeport Music v. Dimension Films, in the 6th District, establishes the rule that any amount of copying is infringement, whereas VMG Salsoul, LLC v. Ciccone in the 9th District rejects that finding and allowed a case of .23 seconds (230 milliseconds) of copying. The "de minimis" doctrine is independent of "fair use" which has a statutory basis, but seems to have arisen from similarity doctrines which are involved in proving that copying took place.