There are some options to consider about FIL's impending visit.
1) Ignore it and make no comments. 2) Call a family meeting with W and daughters to discuss concerns about FIL's visit 3) Oldest daughter goes to her BF's house and you can send your youngest for a sleepover at someone's house 4) Talk with W about your concerns 5) Just have a oh-hum attitude about FIL's visit and comment, "Oh okay...so he's coming on xxxx dates, right? Thanks for letting me know. Do our girls know this? If not, then best to let them know." then right back to your own thing
Funny, one thing about MLCers is that they hate having someone say "no" to them. That raises their hackles BIG time and they'll try to run over you with spewing or just going right ahead and to that very thing just to show you that you're not the boss of them. Very teenage outlook in rebelling against everything: spending patterns, staying out at all hours, hanging out with the "wrong" crowd.
So you have some options before you to think over in the next few days. It is up to you on which one you want to pursue.