Welcome!
Trisquel 8 is based on Ubuntu 16.04. Of the three programs you list, only ZuluCrypt is in the repository of Ubuntu 16.04 and it is as well in the repository of Trisquel 8: the package is named "zulucrypt-gui" (assuming you want the graphical front end). KeepPassXC is not in the repository of Ubuntu 16.04, but it is in the repository of Ubuntu 18.04. I am not aware of any freedom issue with it. That is why I believe it will be in Trisquel 9's repository. On the contrary, not all VeraCrypt is free software: https://www.infoworld.com/article/2609745/truecrypt-or-false--would-be-open-source-project-must-clean-up-its-act.html
