Property-services company ZPG is on the hunt for advertising agencies to work on its Zoopla and uSwitch brands.
The separate but concurrent reviews are going through AAR, with appointments for each brand expected by the end of September.
Brothers and Sisters previously worked with both Zoopla and uSwitch, but declined to repitch.
Matt Charlton, chief executive of Brothers and Sisters, said: "We are very happy to stand behind the successful work we have created for both brands and, as such, we have declined to repitch and wish them well."
Goodstuff Communications, which handles media planning and buying for ZPG, is not affected by the reviews.
Zoopla appointed Gary Bramall as chief marketing officer last year, replacing the company’s first-ever chief marketing officer Gareth Helm, who has since moved to McDonald’s. At the time, ZPG restructured its marketing departments, creating separate teams for the property and comparison-business divisions.
US private-equity group Silver Lake Partners acquired ZPG for £2.2bn in 2018.
Zoopla was founded in 2008 and ZPG acquired uSwitch, the home services comparison website, in 2015.
Alex Gibson, head of brand marketing at uSwitch, and Rich Houston, head of consumer marketing at Zoopla, said in a statement: "Brothers and Sisters have done a great job for us over the last few years and we are grateful for their passion and enthusiasm.
"Both brands are, however, competing in highly competitive marketplaces and we feel that we could benefit from a fresh set of eyes looking at the opportunities that exist for each."
ZPG also owns consumer brands PrimeLocation and SmartNewHomes, software brands Alto, Jupix and ExpertAgent, and data businesses Hometrack and Calcasa.