Walking on eggshells

How do you stop your children from telling their dad everything happening in your home. My kids loyalty is not to me, it’s to their dad. Their dad wants to take them from me because he doesn’t like my husband. They tell him everything that is said and done in my home. Personal conversations, everything. I feel like I’m still living with my abuser and if I’m being honest it makes me not want my kids here. If they think the grass is greener on the other side then go, because I can’t live like this. My kids are 14 and 16. Old enough to be left home alone. If I go out to dinner somehow their dad knows. I’m assuming he calls and asks what they are doing, and where is mom and they tell him I’m out. Then during an argument he will twist things and say “since you leave these kids home alone all the time.” I noticed recently my son will text me and ask when I’ll be home, where am I etc. even though I already told him before leaving the house that I’m running to the store or doing this or that. I’m guessing he’s doing that to get info for his dad. How do I handle this?