He cannot make it up to them by changing the resources your children receive from their father. It is not your ex-spouse's job to make up for this loss, nor should your children be deprived of the relationship they have with their own father because of it. Sensitivity and compassion are required, but this can only happen if the family recognizes the loss that your husband and his children have endured through sharing feelings and talking about the pain. Room for grieving should be observed, however major responsibility for working through this grief needs to be shouldered by their father. The children that have been born out of the union of yourself and your current husband represent a blending of the two families.
Reality explodes fantasy.
Even if the fantasy is based on good intentions. Stepfamilies must progress through their own histories in order to blend together. Ask your husband to go to individual counseling regarding his feelings of loss from his first marriage. Addressing his guilt, pain and ambivalence about the marriage before and after his wife's death are critical pieces to the puzzle. You may also want to do some marital counseling after he has faced some of these issues on his own.