@Cerberus13 said:
The condition is that your spouse MUST also be an applicant for the visa:

Only the first 2 are applicable to you.
That is taken from the calculator though. Actually, not sure if it's possible to leave the declared partner and just not claim points. But take note that a partner visa costs AU$8000+, and if your wife just applies for 189 on her own (if it is at all possible), there is no guarantee that she will be invited.
It is possible to leave the spouse out and not claim points while still being part of the visa application once invited as migrating family member.
Though, if I can recall, the family members would still be asked for proof of functional English in the end. Saw some posts here before of similar case.
For the budgetary concern, I'd agree that the best option is to have everyone in the visa application in one go. They can initially choose not to join the move and do it at a more convenient time later on. Kagandahan nun, may visa na sila. Mas magastos yung subsequent applications kasi.