The joplin-vieweb web interface (forum thread here) exists. It may be difficult to set up and I don't know if it solves either use case.
For Yomitan: desktop alternatives, mobile alternatives, apps like Textbender, and using Yomitan on files converted to HTML are all options to try pairing with Joplin.
For Joplin on other computers, look into Joplin Portable. This thread helps explain how it could work for your use case.