Under what circumstances is it necessary for a dependent applicant of I-526 to file an I-824 application?

You should have included I-824 in your application to adjust. You need to file I-824 with the USCIS so that the agency can notify the US Consulate as the DS-260 application is being processed because this is a case of ''follow to join.'' Also, be aware that there could be a delay which may affect the processing time of DS-260. Moreover, work with your EB-5 attorney to make sure all necessary documents are put together for both applications.

Unfortunately， it is needed if she is processing at the consulate rather than an adjustment.

If your wife did not file for I-485 with you in the U.S. and is processing via consular processing, then you should file the I-824 to notify USCIS of her consular processing.

If your wife is abroad, you need to file an I-824. You should have filed it together with your I-485.

Is the National Visa Center of the State Department processing the case already? If so, you might not have to file the I-824. If not, you should file it.

Yes. You do need to file the form I-824 in order to notify a U.S. consulate through the National Visa Center about your adjustment of status to permanent resident in the United States, so that your spouse and children may accompany or follow to join you.

Yes; you, not your wife, need to file an I-824 to ask USCIS to notify the Department of State (U.S. embassy or consulate in your country) regarding the I-526 approval and your I-485 adjustment of status. In that way, your wife can begin the immigrant visa processing part of her immigration to the United States. USCIS currently is taking 6.5 to 19 months to process an I-824, with most of the I-824s being processed at the earlier range of that processing time.