Praise be to Allah.
It is permissible to sell cartoon movies that do not contain anything that is not allowed according to Islamic teachings, such as deviant beliefs or promotion of immorality, or music.
As for those which contain music, if it is possible to remove the music from them, it is permissible to sell them, otherwise it is not permissible.
Making copies of these movies and selling them is subject to further discussion, because they belong to companies and you need to find out whether or not they allow copies to be made.
If the owners and producers of these movies have stated that all rights are reserved by them, and that is not permissible to make copies of them for public broadcast or personal use, then the basic principle is that we must abide by this condition, because the Prophet (blessings and peace of Allah be upon him) said: “The Muslims are bound by their conditions.” Narrated by Abu Dawud (3594); classed as sahih by al-Albani in al-Irwa’ (1303).
See also: Fatawa al-Lajnah ad-Da’imah (13/188).
If they have given permission to make copies of them, or the owners have put them on the Internet to be downloaded, then there is nothing wrong with making copies of them and selling them, unless they gave permission to make a copy only and not to sell the movies.
If these movies belong to companies that are waging war on Islam and the Muslims, then there is nothing wrong with copying them and selling them, because they and their property are not protected [under Islamic law].
If you are going to work on old cartoons, and you are putting effort into removing the music from them, then what appears to be the case is that it is permissible for you to make copies of them and sell them in return for your efforts, because when there is music in them, it is haram to sell them.
For a more detailed discussion on copying movies and software, please see the answers to questions no. 95173 , 81614 and 52903 .
We ask Allah, may He be exalted, to heal you and grant you well-being.
And Allah knows best.