Sources

1) Source: Genealogia comitum Flandrensium ex libro Florido et Chronico Aldenburgensi, etc "Proh facinus! Fides data negliture, setentia electionis mutatur et alius comes theodoricus de Elsaten filius filie comitis Roberti Frisonis superinductiur. Divisum est autem regnum non in fratres sorte hereditaria sed in hostes lege contradictoria, unus tendit in alterum, Theodoricus in Willelmum, ille se et suos defendens fortiter repellit in se tendentes." (Data from secondary evidence)
2) Source: Genealogia comitum Flandrensium ex libro Florido et Chronico Aldenburgensi, etc "Theodericus, filius ducis alsatie et Gertrudies filie Roberti Fresonis, primi (succesit)" (Data from secondary evidence)
3) Source: Genealogia comitum Flandrensium ex libro Florido et Chronico Aldenburgensi, etc "Cui succesit balduinus comes hanonie, nepos ejus, postea constantinopolitanus imperator et duxit filiam comitis campanie, nomine Mariam, ex qua genuit duas filias Johannam et Margaretam." (Questionable reliability of evidence)
4) Source: Genealogia comitum Flandrensium ex libro Florido et Chronico Aldenburgensi, etc "cui successit Magareta soror ejus, uxor comitis Balduini Hannonie; obiit anno Domini M C XCIIII et in ecclesia sancti Donatiani sepeliture". This is following Philip, described as son of Theoderic (Data from secondary evidence)
5) Source: Genealogia comitum Bulonensium A short genealogy connecting the early Merovingians to the later counts of Boulogne, written circa the 11th century. The earliest generations are almost certainly fictional. Considered a reliable secondary source for generations from Arnulf of Metz onwards. Considered a "primary" source for events from the year 1000 onwards.. External Link
https://www.dmgh.de/mgh_ss_9/index.htm#page/300/ (Data from direct source)