Well, since they’re your posts, you should be able to edit the post. A few things that need to be cleaned up:
Remove all HTML, and convert it to ‘markdown’. I use HTML to Markdown Converter
Then, you need to fix the inline images, since the markdown tags are not used, and interfere with the formatting of the post.
For YouTube videos, you need to remove EVERYTHING from the iframe tags except the youtube URL itself. Then they just embed correctly.