Swagger, I know it's a big step for her to move out. It was depressing for me when my XW moved out (even though I wanted her to at that point).
I think this will be good for you. Don't feel responsible for S5. Your W is the one who is making this happen. Give S5 as much love as you can. Have you and your W discussed telling the kids?
Me-47,XW-43 S13,S16 M:18 BD:4-23-17 W filed:7-17-17 (5 months of in-house separation hell) W moved out:1-6-18 D granted:2-15-18 Decree signed:3-29-18