The book doesn't follow the lineage of Daniel and Harriet. TC H'berg's will is in the appendix. He names the two children as Francis Morrison/Morison and Nancy Ketherine McDonald. He refers to then as "my two grandchildren". I think you could safely assume the children were of his bloodline. I'm sorry I can't give you more than "safely assume". If they were the children of Harriet Carroll would he have given them a bequeath? Some of the other H'berg researchers might have more info than I.