Gaining full custody, what do I tell my kids?

I got divorced last year, to a woman I had 5 kids with. One is an adult and lives with his girlfriend. The other four are 12-16, older kids. After the divorce I moved out of the home we lived in together and custody started at 50/50 per our court agreement. Our house was to be sold, and it was eventually earlier this year. The proceeds were split 50/50 plus my ex getting an extra $12k per our divorce agreement. Now, my ex wife is unemployed, and has been since our 16 year old was born. So when the house was sold she was struggling to find a rental, and was refusing to pay the year in advance, which was easily doable with her money from the house. I’ve had functional full custody of the kids since then. After a month going to different Airbnbs she finally moved in with her parents, an hour and a half away. Today I got the call that she hasn’t found any employment and will be looking to give me full custody or at least alter our arrangement significantly towards me having primary custody. I’m not sure what to do, or what to tell my kids. They’ve been pretty stoic once they got past me and mom not living together, and being with me pretty much full time since the house sold . But still, I can’t see this being received well.