"Thurstan Hrolf" Rollo "Bigot" is not mentioned in the early sources, and any connection to Hrollaug Ragnvaldsson seems to have been created later.

From The Conqueror and his companions, Volume 2 By James Robinson Planché (paraphrased):

Rongwald (Ragnvald) had several children by a favorite slave whom he had married "in more Danico", and one of these was Hrolf Turstain, who followed his Uncle Rollo into Normandy and secured the hand there of Gerlotte de Blois, daughter of Count Thibaut de Blois et Chartres. Hrolf was "the foundation of this branch of the great Norse family in Normandy, and the stock from which descended the Lords of Briquebec, of Bec-Crispin, of Montfort-sur-Risle, and others who figure as companions of the Conqueror."

The third son of Hrolf Turstain and Gerlotte was Ansfrid the Dane, the first vicomte of the Hiemois (aka Exmes). His son Ansfrid II (called le Goz) was father of Thurstan (Turstin) le Goz, a trusted aide to Duke Robert of Normandy who accompanied him to the Holy Land and was entrusted to bring back to the Abbey of Cerisi the relics the Duke had obtained from the Patriarch of Jerusalem.

-----------------------------------

http://freepages.genealogy.rootsweb.ancestry.com/~mainegenie/STANHO... From the work of Michael Stanhope:

HROLF TURSTAIN (HALFDAN 1, EYSTEIN 2, HALFDAN 3, IVAR 4, EYSTEIN 5, RAGNVALD 6, HROLLAGER 7)

b.c.885

m. GERLOTTE de BLOIS (b.c.895, d.c.950), d. of Theobald, Count de Blois et Chartres and Richilde de Main/Bourges (grand-daughter of King Charles II) d. 962

Hrolf Turstain followed his uncle [Rollo] to Normandy, via Flanders, and founded the important Norman families of Avranches, Briquebec, Crispin, and Montfort-sur-Risle.

Issue-

I. ANSLECH de BASTEMBOURG, a.k.a. Oslac de Briquebec- b.c. 910, m. GILLETTE de BEAUMONT (b.c. 922, d. 960), d. 974

II. Ansfrid I. The Dane- b.c. 915, m. Helloe de Beulac (b.c. 942, d.c.1000), d. 978. Ansfrid Le Danois, qui fut, suivant quelques historiens, le premier vicomte d'Exmes ou d'Hyesmes. Il conserva cette charge jusqu'en 978, époque où la vicomtefut temporairement eulevée à sa famille et donée à Roger de Montgommery, grand-père de Roger, qui fut plus tard comte d'Alencon, ainsi que d'Arundel et de Shrewsbury, en Angleterre.'

III GUILLAUME de BEC- b.c. 918, m. BERTHA de VERMANDOIS (b.c.920, d.c.990), d.c.1000