We just separated and my kids don't want to spend time with his new partner. She was a secret affair, and they are 10, 12 and 14. So they feel a bit cheated on as well. She insists on being at every meeting with the kids. She walks 5 meters ahead of him to the meeting. He follows behind looking weak. The kids refuse to go near them because she turns up when they think they are just going to see Dad. What do I do?