can i delete unused themes

Some of those themes might simply need updates to satisfy the Wordfence scans, and yes, I sometimes just remove and re-install a plugin to get rid of those “warnings”. Also, keep in mind that some plugins occasionally get “quiet updates” that will clear in a few days after an actual update notice has been sent out and acted upon.

Can I just delete those wordpress themes [ I don’t even use] from the page within wordpress under appearance, themes…and should I also delete those theme directories from my Bluehost server…?

You need to have at least Twenty Twelve there for possible troubleshooting at any given time, and you might as well have Twenty Thirteen since it is the latest default theme. What I would do there is to delete all themes other than the one/s you actually need…and keep in mind that your custom theme will need its parent if it happens to be a Child Theme. But after deleting all the ones you do not need in order to keep the site running, re-install fresh copies of Twenty Twelve and Twenty Thirteen…and no, you will have have to delete any theme at the server since the dashboard action will take care of that.

But if for some chance it was a child and I deleted 2012 and then reinstalled it would my site be down or not function properly until it was reinstalled…

Even though that is no longer a concern here, it might some day be helpful for you to know an activated Child Theme will have a line beside it there on the Dashboard saying, “This child theme requires its parent theme, (whatever theme).” And yes, things would certainly be a mess without one! But overall, never panic. If your Dashboard ever turns completely white and your site looks like a text-only BB from the ’80s, a fix is still possibly just a few clicks away via FTP/SFTP.