Is it permissible to include the maternal aunt, who has no offspring, in the reward for memorizing the Holy Quran along with the parents, based on the noble Hadith which mentions crowning the parents of the Quran memorizer with a crown and two garments on the Day of Resurrection?

It is permissible to include the maternal aunt in the reward for memorizing and completing the Quran. As for the reward designated for the parents, it is for what they expended in teaching the child. The maternal aunt can hope for a share in the reward if she encouraged and assisted in that.