Is Zachery still up when you are trying to put Chelsea to bed? We had this problem with Tori when Liam was just a baby, she would do her nut if we tried to put her to bed and he was still up- so I used to get DH to take Liam into his room and pretend to put him to bed, and then once we had Tori in her room ready for bed, we would bring Liam back out. We only needed to do it for a little while and she got over it, I think she got it into her head that she was missing out on something by having to go to bed.