I think Berri and Ringo are quite trustworthy. Just because they could transform by accident or on coincidence doesn't mean that they are the bad guys. They seem like nice enough girls anyways.
And I think Berri was zapped by the red light. Well, we aren’t exactly sure because the manga is only in black and white, but she was zapped by the same statue of the cat like the other five were, so I’m assuming the light was red too.
As for Ringo, she managed to transform by her pendant that had a Mew Aqua in it. I think at one point in the game, she was hugging Yuki and the pendant starting glowing and Yuki started glowing too, so maybe that’s how she got infused with her DNA. And in the bit where Yuki got hurt and Ringo was upset, she managed to transform because of her emotions. Rather a bit like how Masaya could transform into the Blue Knight. He was desperate to protect Ichigo and, mixed with the Mew Aqua that was instead him, he was able to transform into the Blue Knight.