I'm in the same situation. I took my son's 12 gauge, .22 and 243. They were never in his name anyway. They now live in my gun safe, 1100 miles away from him. My ex also gives into every request that our son makes, no way in heck I will allow her to have the guns in her house.
You're doing the right thing. It's the tough love thing that most ex's are not willing to handle.