System Definition > Templates application module is restricted by role "admin".

This is Out-of-Box.

You can modify the module definition to allow one of the roles you're giving to also access that module (you'll also have to modify the base application "System Definition" to add that role as well, or the Application itself won't be visible).

However, I don't recommend the modification, as you may then have upgrade issues later on...as that Application module will be skipped in future upgrades.

If you do not want to give the user "admin", then they will have to edit the templates on the Forms themselves, by toggling the Template Bar at the bottom of the form by clicking the "..." more options in the header of the form.   See here for more information:   Templates

-Rob