They sang the Calamari Inkantation, But didn't the squid sisters write the Calamari Inkantation? The Squid Sisters weren't alive at the time, because Craig is the squid sister's father.
The squid sisters revamped the Calamari Inkantation into a modern song, but they didn't write it! Sunken scroll #23 in the first game talks about how it's a traditional inkling folk song from long ago