So MVG - I get the fear - I really do. I live in a 50/50 no-fault state - and while I have have my daughters a majority of the time (which is what XH wanted), every time he hints at a job change or some other move, I feel that fear it's a prelude to change in custody. So - I've felt the fear.
You have a 50/50 agreement and a signed divorce agreement. The fact that your XW has purchased a house and now has potential step siblings that probably will live with them do not seem like compelling reasons to change a custody agreement - your attorney can give you a better idea about the family court judges in your area.
You are doing the right things, establishing yourself as Den Leader, asst. coach etc. Look for opportunities to volunteer at their school as well - get to know their teachers etc.
Your XW may very well try to set up OM's daughters as their "sisters". That's not the worst thing in the world, MVG. And new "sisters" do not equate to a new "dad".
