Isembard Took was the son of Gerontius Took and Adamanta Chubb. He was born in T.A. 1247 and died in 1346. He had numerous siblings: Isengrim III, Hildigard, Isumbras IV, Hildigrim, Isembold, Hildifons were older than him but, Hildibrand, Belladonna, Donnamira, Mirabella and Isengar were younger than him. It is unknown who he was married to but he had a son, Flambard Took in 1387.
In the first draft of the Took genealogy Isembard was named Isambard, second son of Gerontius and born / died in 1237-1335. He had no children.
In the second draft Isambard and Flambard, who at that time were third son of Geronius, were reversed thus Isambard became the third son while Flambard the second.
In the third draft Isambard were renamed to Isembard and reinstated as the second son. Flambard became his son and Hildigrim the third son of Gerontius.
In the fourth draft Isembard were removed to the seventh place of the heirs of Gerontius with the birth and death years as shown in the LotR.