I would probably work on them separately. It is difficult now, I understand that, but in the long term maybe it could work. Then, I would probably try to work in is, trying not to stay with them while they fall asleep. If B gets out of bed, I would do silent return. In this way, you would avoid to be engaged. It would probably take lot of time and effort the first nights, but when he understand there is no fun involved, it should be quicker(if he's not ut, and the routine is ok). When he's asleep, if K is still awake, i would send him in his bed. If he's asleep, I would transfer him. Does K sleep independently or need you to fall asleep?