Re: Yahoo transfers disabled
As Bruce mentioned, PG Offline is a good choice. If it is still working then it is able to download all Y!Group content, including members, messages, files, and photos.
There are also member and file download tools on YahooGroupedia:
These are extensions for the Chrome browser, and require a bit of technical effort to install and use.
And, of course, if your group has 1000 or fewer members you can directly export the list as a CSV file from the Actions menu on the Manage Members page.
All of these methods leave you with the problem of uploading the content into your Groups.io group; except for the Members list - for that you can use Direct Add (if your group isn't Premium you could use the one-month of Premium option, for $10.).
More Help: https://groups.io/g/GroupManagersForum/wiki
Even More Help: Search button at the top of Messages list