How to add Post Activities to Email template and send email to multiple contacts with a workflow?

Hello,

I think the title is pretty self explanatory... 

Context: When we work on a Case, on certain conditions, a workflow is triggered to send an email to the client so he is kept updated. We use an Email template so the process is automatic.  We're using CRM 2015 on-premises.

1) We want the comment history to be in the email. Is there a way to put "Post activities" in the template?

2) We also want to send the email to all people in the company that have opened cases, not only the Case's current contact. Is it possible to send an email from a template and through a workflow to multiple contacts?

Thanks!