How to embed all comments and comment form to other website
I think the best solution is to expose the comments as a REST resource on example1.com. You can achieve this with the services module (you will probably have to create a custom resource).

Then on example2.com execute a GET request on the REST resource and display the comments.

Edit: If you want to fetch the comments per node you will have to add a query param to the resource containing the node ID for which you want to fetch the comments.