Is it permissible for parents to perform the Hajj pilgrimage this year on a visitor's visa, and is it permissible for the questioner to accompany and serve them during Hajj without performing the rituals, knowing that he has already performed the obligation previously?

If your parents are physically and financially able to perform Hajj, they must initiate it, and you should accompany and assist them. If you accompany them without the intention of performing Umrah or Hajj, it is permissible for you to enter Makkah without ihram, according to the most preponderant opinion among scholars. However, it is better and more virtuous for you to enter in a state of ihram.