Complex sentence: When her wealthy parents, Bill and Rita Thornton, learn about this and visit her, it is the first time that Leo meets them, and they are not happy about Leo taking their daughter, and not telling them about it.
Split into simpler sentences: When her wealthy parents, Bill and Rita Thornton, learn about this, they visit her. This it is the first time that Leo meets them, and they are not happy about Leo taking their daughter, and not telling them about it.