The acts, who were both mentored by Walsh when they were on the show, have expressed an interest in returning to the series as mentors.
Walsh has previously worked on the show with Ronan Keating and members of Westlife.
Other special guests rumoured for the Judges' Houses stage include Robbie Williams joining Gary Barlow and Beyoncé being reunited with her Destiny's Child bandmate Kelly Rowland.
Sinitta revealed to Digital Spy last month that she would definitely be involved in the UK or US X Factor at some stage, but it is not clear whether she will have her usual mentor role now that Simon Cowell has departed the ITV1 programme.
The X Factor auditions concluded in Liverpool this week.
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