Kovod for one’s parents, stepparents, older siblings, and virtually all human beings, should not be a question to be paskened. It should be show to all. You and I have no mandate to LOVE a stepparent, but out of respect for our own parents, we should always be respectful of the person to whom they are married. If it were always an easy thing to do, this question would not have been asked. Sometimes there is great resentment of the “step” for literally stepping into the place of the parent who is out of the picture, whether through death or divorce. Children of divorce often harbor the belief that the parents will get back together BUT for the interloper who has taken mom or dad’s place. Irrespective of whether or not that belief is realistic, respect must be shown, if only to make the parent happy. In the case where the step might have been directly responsible for the breakup of the marriage, something which we do unfortunately see (though rare in the frum world, it still does happen, chalila), then I would say the children should refrain from contact with the stepparent, if they understandably feel they cannot be civil.
My dear daughter-in-law just lost her step-father suddenly this past month. Her bio dad is alive, B”H, and in her life, but it was her stepdad, whom I truly considered to be my dear mechutan, who was largely responsible for her sister’s and her upbringing. He was a great dad to them, and her loss was immeasurable. BUT, because her own dad is alive, she had to refrain from certain expressions of her grief, and felt like she didn’t belong anywhere, while her mom and his birth children sat shiva together. I believe that children can and should show honor and respect to a stepparent. It should not even be a question.