I'd put them in the same room (if they're not already). That way you are right there with them both - its what I used to do with DDs 1 and 2. I would stay in their room for however long it took - and at the beginning it was looooooooooong. Otherwise, if I had to go between one and the other there was just no chance. Now I have to get DDs 1 and 2 to bed, and then tackle DD3 - usually involving the occasional walk back into 1 and 2's bedroom to tell them to be quiet and get back into bed while #3 is feeding.