Summarize this article in one sentence.
If you know the wedding is a fraud, or there are legal reasons the wedding should not go through as planned, you have at least 28 days to take legal action. Couples must let a registrar know of their decision to get married and the registrar is required to make that information public for at least 28 days.  Laws vary by jurisdiction, and each case is situation. Call or visit your local courthouse to discuss the steps you need to take once you have legal reasons the couple cannot get married. If you have a good reason to believe the wedding should be stopped it will help if you get others to feel the same way. If you feel it may be your only way to stop the wedding, share your research you've done with the family and friends of the couple to obtain a greater opposition. Use this pressure to divide the couple.  This should be done as a last resort as it could be very traumatic, or it could actually bring the couple closer together in their possible attempt to escape and elope. Crashing a wedding is not advised. It is a dramatic and reputation-damaging route which may not even work since some couples are legally married by signing the marriage license before the wedding ceremony. The recommended plan would be to talk way ahead of time with the couple to avoid expenses and chaos and to have a rational discussion where you all share your sides. If the couple are relying on both or one set of their parents to support the wedding, you may want to try to stop the money source so the wedding will be called off. If you have legal reasons, again, share this with the parents and let them know they may be financially supporting a harmful situation. If there aren't legal reasons you can still voice other concerns and attempt to stop the money flow.
Call out the lies. Involve others. Follow the money.