1) If the monologue was published in the US and without a valid copyright
notice, it's in the public domain. If the monologue was published with a valid copyright notice and the copyright was renewed in the 28th year after the work was published, then the copyright will last for 95 years after the date of publication (i.e. until the late 2020's) You may need t located the original publication and look for a copyright notice. In addition, unfortunately there is not straight forward way to ascertain whether the copyright was renewed in the 28th year.
If the monologue was published outside the US and it was published with a valid copyright notice, its copyright term is 95 years after its publication date. If the work wasn't published with a valid copyright notice, it is either be in the public domain or its copyright will have been restored. (It's pretty likely that its copyright has been restored.)
If you're in the US 9th Circuit District, there's a good chance the monologue will be treated as an unpublished work. (That is, the copyright term will be life of authors + 70 years.
The recording by Stanley Holloway is copyrighted only as to the recording itself not the underlying lyrics. If the recording was published without a valid copyright notice, it's in the public domain. If, however, the work was published with a valid copyright notice and the copyright was renewed in the 28th year after the work was published, then the copyright will last until 203.
2) Generally speaking it is not legal to change the lyrics to a song without permission from the copyright holder. Changing the lyrics creates a "derivative work
" (i.e., a new work based on the original). Only the copyright holder has the right to create derivative work. However, the adaptation of the lyrics can be considered as 'fair use
' if the new version is parody, a satire or criticism.
3) All three works are in the public domain
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