Roles in DT Theme

Hi,
I use DT Responsive Theme and Newday Child Theme.
I have a problem with the standard wordpress user roles. It seems (i read this on the forums here) that DT Theme allows only 2 roles (Admin and User). My site needs to have others roles like “Author” since it is a collaboration site. Some members must have the ability to publish and edit articles and posts.
Actually the wordpress admin bar only appear for the “administrator” role not for the other roles.
Since DT Theme has only admin role, is there a solution to create other roles. I tried different User Role Plugins without success.
Please help…
My site : https://aclnet.fr/CMA_FR
Thanks for your answers

Alain