function getUsersFromGroups(groupEmails) {
  let users = [];
  for (let groupEmail of groupEmails) {
    let groupUsers = GroupsApp.getGroupByEmail(groupEmail).getUsers();
    for (let user of groupUsers) {
      if (!users.some(u => u.getEmail() === user.getEmail())) {
        users.push(user);
      }
    }
  }
  return users;
}
Get indirect members from multiple groups (and delete duplicates).
@param {array} the e-mail addresses of multiple groups.
@return {object} indirect members of multiple groups.