Asalamualaykum Wr Wb

This isnt a fiqh issue.

Musical instruments are Haram. If you were to sell it or give it to some one else, then you would be facillitating that haram and would be sinning everytime that person used that musical instrument.

Same with if you had some weed and stopped smoking it and sold it on or gave it to some one else, you would still be sinning in that.

Allah swt tells us to forbid the wrong and enjoin the good. Infact its an order, its duty upon the Muslims. Dont think about the money you will gain from selling it, because the rewards for you trashing the instruments and disposing of it so that no one else can use it are far greater then the value for it in the dunya.

It can be hard to throw away such belongings of ours, remember that Allah swt will grant you something greater.

We hate what Allah swt and his rasool saw hate and love what they love.