Just breath, remember this will pass, you just need to hang on and don't give in! Keep doing whatever you can to cut him out without responding directly to him (or his family, from the sounds of it), because he ain't listening and you know you'll just be feeding him. Sever the ties like cutting tatami. Breath and focus. Keep venting in here if it helps you de-stress and re-center yourself, we're happy to provide ears to listen and support where we can.