I just rewatched "Forever Charmed" the other night being bored and all. And it hit me that another instance of lazy writing and plot holes occurred. At the point of the episode where adult Wyatt & Chris appear claiming Wyatt had lost his powers doesn't make sense.
Back in season 4, when we are first introduced to the Hollow the Source used it to take Piper and Paige's active powers. Both good and evil had to come together to banish the Hollow which happened to be Phoebe and the Seer. Once the Hollow was banished Piper and Paige's active powers were immediately restored.
However in season 8 not only are Piper, Patty and grams capable of banishing the Hollow which is a plot hole in itself. But Wyatt's powers weren't restored after the Hollow was banished. Billie & Christy possessing Wyatt's powers shouldn't be a factor since the Source possessed Piper and Paige's when he had the source take them.
If Chris & Wyatt appeared before Piper and Leo went into the past claiming he lost his powers that would have made sense. Or better yet just have both brothers at the end making a potion.