I just double-checked and you are the administrator for umltransformational.wordpress.com, so you do have the proper permissions to add users.
You should have a Users tab in your Dashboard in which you can invite others to participate on your blog at different levels. I see one person has already been invited as a follower, so you can just follow that same process for the others.
These two pages explain the process in more depth:
If you are having difficulty using that page, make sure you have third-party cookies enabled, and you might also try a different browser to see if that changes the performance of the page for you.
If none of that helps, please reply back with a more detailed explanation of what is failing on your end. For example, after all of that, are you still unable to use the drop-down menu for Role? Are you able to invite people but they aren't able to accept? And so forth.