Juggling one household’s bills isn’t easy. Juggling two? Families say they need all the help they can get. Cala Nanda’s family worries about two property tax bills, one for the Highland Park home she owns with her husband, and the second for her father-in-law, who lives in a home next door. “My father-in-law is now 92 and he lives by himself. My husband is there every day helping him out,” she said, noting that while her widowed father-in-law’s fixed income covers his expenses, living next door allows him independence without hiring expensive professionals. The senior Nanda pays more than $9,0…