Ronan was skeptical about trusting the witch, skeptical that he would be truthful and skeptical that they even needed it. But he went along with it, knowing that in order to spend time with his brother and get to know him, like he wanted to, he'd have to placate the boyfriends or he wasn't going to be allowed close. And it was understandable that they were so protective. Mickey had, after all, been kidnapped by the warlock at one point. Someone showing up out of the blue claiming to have come from the same place must sound awfully suspicious.
When Barclay gave him the clear, he smiled at Mickey, then at the boyfriends. The smile faded some at the witch's addendum. "My motive is to get to know my brother! To have him in my life finally." He looked from one face to the other and let Mickey put the bandaid on. "I swear, that's all I want."
Leon still looked unconvinced but there was little he could do at this point. He glanced at Andrei, then turned to Mickey. "I guess he can stick around."