Trying to "suddenly" update something that's years out of date to a current[ish] version is always fraught with weirdly closeted skeletons

At this point, I'd probably do

- mysqldump of each site

- mysql import them on a new server

- setup however many instances of wordpress I needed

- connect all those instances to the imported databases

- click "upgrade database" (or similar) ... and hope for the best :)

Alternatively:

- generate a non-limited RSS feed of the whole site (not capping at 5 or 10 entries, but every entry)

- import into a different blogging platform via that rss feed