Hi CeeEee2,
To get the thumbnails in the excerpts, you need to use the “Featured Image” function. To get the image to show up in the post, you use the “Add Media” function. So, basically, if your using the excerpts you need to set two images for each post. One for the page (Add Media) and one for the excerpt (Featured Image). If you do that, you shouldn’t really need to use a plugin at all.
That’s what I’ve done for my website, anyhow. Give it a go and see if it works for you. 🙂
Regards,
Sharon