Curtis' grandmother lives in the retirement home, and also is a satanist.
Jenny's father Pat had been stashed in the retirement home ever since he was abducted and poisoned, and had turned comatose as a result. Jenny found him there while researching the presence of the Satanic Cult, but they were both captured and locked in a closet.
When Todd, Curtis and Hannah came to save Jenny, minion Bob had used The Book of Pure Evil to wish for real food. The side effect here was that everyone who ate it became so hungry that they'd eat people. The Gang had to help Atticus fight off cannibalistic old people.