This past episode was obviously hard to watch, but I think the worst part was hearing that Kody did not reach out to Savannah for Christmas. We obviously don't know the details of her relationship with her dad, but I assume there is a good chance Savanah would have gone with Truley, Mykelti and Ysabel to the post-Christmas celebration at Robyn's house.
Despite what is going on between Kody and Janelle it is absolutely Kody's responsibility to step-up to foster and maintain a relationship with his children, especially those who are minors. If anyone treated Robyn's kids this way he would lose his f'ing mind.