The latest series of the hit Channel 5 show has been dubbed All Stars and New Stars, as former contestants are joined by other celebrities making their debut on the reality television programme.
The reality TV couple, dubbed "Speidi" by their fans, competed in the 11th series of the show as one housemate in 2013.
Montag, 30, and Pratt, 33, said they are on a mission to "make Speidi famous again".
In 2009 Pratt was baptised by Stephen Baldwin and a video of the event was posted online.
When asked for her 'likes' before entering the house Montag listed Jesus as her choice.
In September 2016 she told the FaithWire website that the couple were trying to get pregnant.
"You know I had to pray to get my husband to even agree to have a kid," she said.
Many have accused the couple of faking their Christian faith to gain a bigger following in the United States after they lost most of their fortune.
But she rejected that and said: "Because of God, I was able to rebuild and refocus.
"I try to prioritise prayer time every day, at least once a day, try to listen to all the Christian music I love and preaching every day and just keep it part of my daily life because if you don't keep it part of your daily life, it slowly kind of slips away from you, for me at least, I have just reprioritized that and honestly that is my life."
Other celebrities to enter the house include Ray J, Calum and Angie Best, footballer Jamie O'Hara, Loose Woman Coleen Nolan and model Jasmine Waltz.
