Login path per user

You can actually assign the login path per user - insert "!host_uid" and/or "!invited_uid" somewhere into the login path, and users will be directed there.

I don't want to introduce login paths by user roles, because those can be more than one per user, and then I'd need to know the role separator character and if roles should be replaced by their role ids or their actual role names, and so on. Instead, if the uid replacement doesn't suffice for your use case, I advise you to set the login path to some custom URL (say, "role-redirect/!invited_uid") that redirects the user based on their roles. You could have a small module that does this, like (not tested):

function role_redirect_menu($may_cache) {
  $items = array();

  if ($may_cache) {
    $items[] = array(
      'path' => 'role-redirect',
      'callback' => 'role_redirect_callback',
      'access' => TRUE,
      'type' => MENU_CALLBACK,
    );
  }
  return $items;
}

function role_redirect_callback() {
  $user = user_load(array('uid' => arg(1)));
  if (!$user) {
    drupal_not_found();
  }

  $roles = array();
  foreach ($user->roles as $role_id => $role_name) {
    $roles[] = $role_id;  // or $role_name, if you prefer to compare against string values
  }

  if (in_array($your_role_id, $roles)) {
    drupal_goto($your_path);
  else if (in_array($your_other_role_id, $roles)) {
    drupal_goto($your_other_path);
  }
  else {
    drupal_goto($your_default_path);
  }
}

Copy this into a role_redirect.module, copy and modify some .info file into role_redirect.info, and you're done. This may or may not work - as mentioned, I haven't tested it at all, it's just a quickly written up sketch. Anyways, even if it doesn't work, this is about the way you want to go for this.