I am sorry to hear about your parents @ufv I had the same too. I never had any visual hallucination about my dad, but I often dreamed of him. I still do nowadays, but very occasionally. The way grief works varies from person to person, those who are more susceptible to hallucinate will experience grieving-hallucinations. Those who aren't might dream of their lost loved ones, instead.
Thank you for your comment and sharing your experience with us :)