I think you need to first get the customers of that group whatever id the group has:
$collection = Mage::getModel('customer/customer')
->getCollection()
->addAttributeToSelect('*')
->addFieldToFilter('group_id', 4);
then after you created the order(the link you mentioned somehow), you should assign each order to each customer in a loop like, create this order, assign this customer to order
$order->setCustomerId($Customer->getId());
$order->setCustomerFirstname($Customer->getFirstname());
$orderbyid->setCustomerLastname($Customer->getLastname());
$orderbyid->setCustomerEmail($Customer->getEmail());
$orderbyid->save();
also there are many extension for assign order to customers, it might not be exactly for customer groups