No family eligibility should be inferred from the size or price of a private purchase. The official joining-family terms concern people, not property units.
Assess the actual joining relatives
The intended eligible spouse and unmarried children under 21 should be included initially under the FAQ. Each adds US$15,000 and a US$1 million gift, including in the corporate route; a property package does not replace those commitments. Family provisions are stated in terms of people and their relationships, so the documents that matter are civil-status documents rather than anything describing what was purchased.
Assemble, for each intended family member, the record establishing the relationship, the identity documents, and any translation that will be needed, and note which of those does not yet exist. Nothing about the size, price or configuration of a private purchase changes who may be included or what each additional person entails; those terms come from the official instructions and must be confirmed there, since they may change. Hypothetical example: a household headed by a land surveyor assumes a larger unit covers additional relatives, and the official terms are found to speak only about individuals and their relationships.
Confirm too who issues each civil-status record and what that office requires from an applicant abroad, because a document that must be requested in person changes the order of every other step. Where a translation is needed, treat it as its own item with its own lead time rather than an afterthought attached to the certificate.