Their testimonies will come the day before an appearance by Peter Goldsmith, Britain's former attorney-general, who dropped his legal objections to the war just days before the invasion.
But much of the week's focus will be on Friday when Tony Blair, the former prime minister, is due to give evidence.
'Hunger for blood'
Jean Seaton, the associate editor of Prospect magazine and the author of an article analysing the inquiry, said the inquiry is getting closer to determining the way in which the government operated in the lead-up to the invasion.
"There is a huge hunger to somehow see blood on the floor. People want the humiliation [of former leaders]," she told Al Jazeera.
"I don't think [the public] knew the detail of how it was that people came to their decisions and how they made their dispositions.
"Seeing Elisabeth Wilmshurst - who is one of the people who acted in a way that is quite controversial - seeing those people and how they arrived at what are always quite difficult judgments will be a very profound backdrop to seeing Tony Blair."
The inquiry is also expected to hear testimony from Gordon Brown, Britain's current prime minister, John Chilcot, chairman of the inquiry, has said.
Brown's scheduled appearance is likely to take place before parliamentary elections, raising concerns that the inquiry could become caught up in party politics.
An initial decision to hear from Brown after the elections had drawn criticism from his opponents, who said the prime minister was trying to avoid drawing attention to his role in the war before voters headed to the polls.
Brown served as finance minister as Tony Blair decided to include UK troops in the US-led invasion of Iraq.
The conflict split British public opinion and spawned a massive protest movement, and much remaining support for the campaign withered away as Iraq descended into chaos.