Changing things like custody would have an impact on child support and so a motion for modification of child support should be made contemporaneous with any change in custody.
The daughter who turned 18 is now emancipated by virtue of turning 18 and you are likely no longer required to provide child support for her. There are exceptions. For example, if you and ex-wife agreed to pay for things like college or support past her 18th birthday. Also, if she is still in high school and on track to graduate before she turns 19, then you would have to continue supporting her even though she is 18 up until she graduates high school.
Please feel free to email me if you have any questions.