Identical twins Josh and Kyle make up the pair, who first appeared on The X Factor two years ago.
The Brooks live with their nan who has looked after them since they were 18, reportedly taking the twins - and their younger brother - from their parents who suffered from drug addictions.
"Josh and Kyle’s parents were ravaged by addiction and incapable of looking after the children," a source explained this weekend.
They told The Sun newspaper: "[The Brooks' nan] Colette stepped in and has been caring for them ever since.
“[Their mum] is proud of all three boys but she is still too sick to be responsible for them.”
Josh is quoted by the tabloid as saying: “We want to make Nan proud because she’s given up her life for us.”
Kylie added: "Our parents were unable to look after us. Our Nan is the rock in our lives. We speak to our parents regularly, but don’t have much of a relationship. Nan has always been a mum to us.”
In last night's show The Brooks were seen singing for the judges at the room auditions and reuniting with former mentor Louis Walsh, as their nan waited on outside.
"We auditioned for the show when we were 15 back in 2014 and got to Louis Walsh's judges' houses in Bermuda," the guys explained. "When we didn't get through we were gutted.
"We can totally understand where Louis was coming from [when he said we needed more time] and there's a huge improvement from those two 15-year-old boys, we're glad to be back... fingers crossed."
Returning with "unfinished business", The Brooks won four yeses from the judges to sail through to bootcamp.
The X Factor 2016 auditions continue Sunday night at 8PM on ITV.