He is the father of writer Ewa Siemaszko, co-author of Ludobójstwo dokonane przez nacjonalistów ukraińskich na ludności polskiej Wołynia 1939–45 (The Genocide Committed by the Ukrainian Nationalists on Polish Citizens of Volhynia in 1939–45) consisting of two volumes of 1,500 pages of research.

It was inspired by the initiatives of the surviving community of combatants of the 27th Volhynian Division of AK, and the apparent lack of historical documentation resulting in numerous misconceptions.

Initially, Władysław Siemiaszko was asked to assist military historian Józef Turowski of the Polish Society of War Veterans, gathering materials for a memorial project.

[3][4] Subsequently, Władysław with his daughter Ewa Siemaszko, in their own ten-year-long research project went on to document murders committed on Polish citizens by Ukrainian Insurgents in some 1,865 villages and towns of Volhynia during the Nazi and Soviet occupations.

Their books were based on witness accounts, court documents including transcripts from trials of Ukrainian war criminals, as well as the Polish national archives and statistical censuses.

However, Marples also noted, that Ilyushin failed to reach a reasonable conclusion in his article and made no distinction between Ukrainian atrocities committed against officials and innocent civilians.