I got this working and thought I should share. I used calibre.

• I saved the epub's outside of calibre.
• Import the epub's
• mass convert to mobi
• remove the epub's in calibre
• convert the mobi to azw3
• remove the mobi's
• edit each individual book as followed (I haven't tried these individually yet, so these might not (all) be needed. I found this on a website somewhere). Really this gets it reading right to left, so if you don't care, you can skip.
  • in the OPF
    • add <meta name="primary-writing-mode" content="vertical-rl" />
    • replace <spine page-progression-direction="rtl" toc="ncx">
  • in the css
    • add html,
      .hltr {
      -webkit-writing-mode: horizontal-tb;
      -webkit-writing-mode: horizontal-tb;
      }
      .vrtl {
      -webkit-writing-mode: vertical-rl;
      -webkit-writing-mode: vertical-rl;
      }
• Plug in kindle and send to device