Images in RSS feed…

Any image included in the body of a post will show up.

Custom fields… you may need something like this: https://www.ads-software.com/extend/plugins/wp-rss-images/

I have tried that plugin, but it still does not pull out the images…

Right, because it doesn’t look in the custom fields, and just the featured image. You’d need to edit the basic logic to know to look for the custom fields. Since YOU are defining those custom fields, you’d have to do the coding here ??

Do you know a good place to start?

Actually yes ??

https://justintadlock.com/archives/2008/01/27/custom-fields-for-feeds-wordpress-plugin