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how can I move all files from each blog to the directory of my single Bluehost hosted site?
Pick one domain to be the MAIN domain.
Move that to Bluehost and convert it to multisite.
Create a site for each mapped domain (sitename.yourdomain.com etc)
Export content from sitename.com and import to sitename.yourdomain.com like normal: https://codex.wordpress.org/Importing_Content#WordPress
Once they're all over, map domains.
Search/replace post content for each site, changing sitename.yourdomain.com to sitename.com
Done.