You are confused all along about non-migrating dependents and migrating dependents.
Non-migrating dependents are people whom you support financially/physically but are not intending to migrate at present. So they are not visa applicants, will not be considered for PR, you just need to mention their name for future references and provide their MC and PC. Later (after you get your PR) if you want them to migrate, you have to apply separately for them as your dependent.
Migrating dependents are the secondary applicants who are included in your application. You and all the secondary applicants will get the Visa at the same time, and all the secondary applicants will go through almost same process (background security check, almost all the documents as yourself) as you. Also you have to provide secondary applicant fees for them.
So, when you express your intention to migrate them with you, with a form 47A you are moving (or adding, if you haven't mention them before) your dependents from non-migrating dependents category to secondary applicants category. In that case, you have to pay the fees and they will make a detail check for your dependents as well.
Then if you again revert your decision and decide that you don't want them to migrate at this time, you can request you CO to move them to non-migrating dependents category again (if they are already converted to secondary applicants).
Under no circumstances you should just hide your dependents in your application. You should either declare them as non-migrating dependents or include them as secondary applicants.
So, I'd suggest first make yourself clear with the definitions and requirements, then decide what you want to do.