Depending on how much time your brother still has, the Annulment -Divorce route may be too slow. You should have him legally transfer his major assets to you or to a trust in which he names the beneficiaries. That transfer will be immediate and not require court approval, as long as he is of sound mind and understands what he is doing and a doctor in the nursing home will testify to that fact, it will be legal.
You can also try the divorce route, as a back up, but that will rerquire court approval and take some time.
If you will be in the NYC metro area, please call me to arrange for a meeting to help you to legally effectuate these recommendations.
Leonard M. Weiner, Esq./Divorce Solutions