Is it necessary to delete an entire post if it contains replies that violate Sharia and only those violating replies cannot be deleted, especially if the post has already spread?

What appears on your personal page of that which is legally forbidden (haram) should be dealt with according to the situation. Either you delete it, or you comment on it in a way that nullifies and refutes it if deletion is not absolutely necessary. If it becomes necessary to remove the entire post, then delete it. Its spread will not harm you if you denounce the evil to the best of your ability.