Is the need for my parents to accompany me to run their difficult errands outside the home an excuse to miss congregational prayer or to perform it outside the mosque?

The Gist of the Fatwa:

For the validity of congregational prayer, it is not a condition that it be performed in a mosque, even though praying in a mosque is superior. Accompanying one's parent may be an excuse that permits abstaining from congregational prayer if refraining from accompanying them would lead to hardship or harm for the parent.