If you will not be physically traveling with your parents, I would highly advise using a skilled TA with experience in booking HI travel. This will cost some money, but it's important that the services you book in HI all understand that they have an ongoing relationship with the TA and depend on the TA for future business and therefore can't disappoint your parents.
If something does go wrong, it's also good to have an experienced TA because you simply call the TA and have them fix the problem rather than trying to handle yourself and dealing with people you have never spoken with before and will never speak with again.