Into a large kettle of vigorously boiling salted water, plunge the lobsters, head first, and boil them, covered, for 8 minutes from the time the water returns to a boil. Transfer lobsters to a cutting board and allow them to cool. Break off claws at the body, and crack them. Remove claw meat and cut it into 1/2-inch pieces. Halve the lobsters lengthwise along the undersides and remove meat from the tails. Cut into 1/2-inch pieces. In a heavy saucepan, cook the lobster meat in the butter over moderate heat, stirring occasionally, for 2 minutes. Add 6 teaspoon Sherry and 3 Tbsp brandy, and cook the mixture, stirring for 2 minutes. Transfer lobster meat to a bowl. Add the cream to the Sherry mixture and boil until it is reduced to about 1 cup. Reduce heat to low and stir in the remaining Sherry and brandy, nutmeg, cayenne, and salt to taste. Whisk in the yolks. Cook the mixture, whisking constantly, until it registers 140° F on a cooking thermometer. Cook, whisking, for 3 more minutes. Stir in lobster meat and serve over the toast points.