Their records belong in the same package as the principal's, even if their flights are a year away: identity and civil documents, relationship evidence for a spouse or child, and immigration history. USCIS issues instructions for Form I-140G supporting documents through the official portal, so wait for those before ordering translations or certified copies in bulk.
Keep absent members' paperwork current
Someone who stays behind for months may need documents that are still valid when their step arrives. Track passport expiry dates, note which civil records were issued long ago, and keep contact details and addresses updated in one place. Decide who in the household is responsible for responding if a request for further documents arrives while the principal is abroad.
A file that was complete at filing can quietly go stale during a staggered move. Add one arrangement that a staggered move makes necessary: decide how a document is produced when the person holding it is in the wrong country. Originals, certified copies and translations all have a habit of being wherever the principal is, and a request arriving while the household is split can turn a two-day task into a fortnight of couriers and rebooked appointments.
Agree where originals live, who holds certified copies on each side, and how a replacement is obtained quickly. Hypothetical example: a household splits with the principal travelling first and carrying the family's certificates, and a subsequent request for a document held in the wrong country costs three weeks — a delay that a scanned index and one set of certified copies would have removed entirely.