Thanks for All the Earthworm Custard - S7.E20

Mel finds out that the children have or had an aunt and uncle in Canada who look suspiciously like Brian and (the original) Sophie. They confront Brian and Sophie, who admit that, seven years ago, they met Josh, Mel and Lucy's aunt and uncle at the children's home – and then, after the aunt and uncle realized that they were aliens, the aunt and uncle were kidnapped and kept in suspended animation in the attic for seven years. The children insist that they let them free. Meanwhile, Wendy discovers Brian and Sophie are aliens, and she tells Pete and Frankie too, so Brian wipes their memories. Everyone realizes that it is time to move on. Josh, Mel, Lucy, Harry and CJ all move to Canada with the real Brian and Sophie Johnson, and the aliens appear to go back home to Valux; however, Brian presses the big red button that caused the pair to crash-land on Earth in the first place setting the stage for series 8. They land by the sea and then head for the foster home.