Didn't Trask consider the possiblity of a little olive branch if Quentin and Charity got together? Also, I believe in Victorian times, it took years to have someone declared legally dead such as the case of Laura. But still, Judith did control the bulk of the money and he reasoned it would be much quicker to get it out of her than wait around for Laura's death certificate or risk a baby interfering with his plans so he has to elminate Minerva, Jamison and Nora.