Father died in 2008, mother died this month. 2 children and grandchildren. One child gets all but a trust set up for grandchildren and a church. Other child not mentioned, but he is a forced heir due to handicap. Can either son open succession even if the favored child who got everything does not need to open succession as it was all left to him? Will the trust need to be reworked to give the forced heir his share?

This will be complicated and you need to discuss it with a lawyer in person. First, the handicapped person has to be 'permanently incapable of taking care of their person or administering their estate.' Second, assuming that that son is being supported by the government, his inheritance will be pretty much wiped out by the state, unless he has a trust. And it's too late to put it into a trust. So talk to a lawyer.