Please review step 5 of immigrant visa process https://travel.state.gov/content/travel/en/us-visas/immigrate/the-immigrant-visa-process/collect-and-submit-forms-and-documents-to-the-nvc/step-5-collect-supporting-documents.html
Check the documents required by the country at https://travel.state.gov/content/travel/en/us-visas/Visa-Reciprocity-and-Civil-Documents-by-Country.html . We brought originals of all the documents submitted. Just make sure that you also bring pictures of your sibling over the years. You should get a visa appointment soon. Maybe it’s delayed because of holidays. I remember I did call NVC to check the status after documents were approved. We had to wait for couple of months before interview date as well. But if you are concerned, ask your sibling to call NVC.