Hello,
Was your cousin killed in real life or in the dream?
Also, I believe you may be an intercessor/watchman for your family. A watchman would alert troops of impending danger and send warning etc. You carry a great responsibility of relaying the truth and being courageous despite possible rejection and persecution. Tornado dreams are common and could signal either real natural disaster OR confusion and turmoil in this case coming at your family. I would go into prayer and cover the specific family members in prayer as well as yourself. Come against the spirit of death, freak accidents and disaster concerning your family. Also, I do not know if you are the only one saved in your family, or if you feel the burden of speaking the God honest truth to your family, but I’ve been there. Stand firm in the faith, do not compromise and ask God to give you strength to live a bold right life! Also, I would pray Psalm 91 every day concerning yourself and your family until you see manifestation/breakthrough.

Blessings!

Hope this helps. Blessings!