The photos display on the page, but not on the thumbnail. Odd, I'm not sure. I've never linked from a FB URL before.

You can try copying the image link to this free site. I've tried it before and it works fine. Log-in is not required, but not sure what copyright they will have on the photos you use with their site.

I would then copy the markdown URL and paste into the Steemit post. You should be able to edit the post. Don't edit often though, you will lose bandwidth! That will limit your time online. I advise to edit this time because your intro post is important.

https://postimages.org/