Aftermarket Afterlife by Seanan McGuire

Seanan McGuire's New York Times-bestselling and Hugo Award-nominated urban fantasy InCryptid series continues with the thirteenth book following the Price family, cryptozoologists who study and protect the creatures living in secret all around us
Mary Dunlavy didn't intend to become a professional babysitter. Of course, she didn't intend to die, either, or to become a crossroads ghost. As a babysitting ghost, she's been caring for the Price family for four generations, and she's planning to keep doing the job for the better part of forever.
With her first charge finally back from her decades-long cross-dimensional field trip, with a long-lost husband and adopted daughter in tow, it's time for Mary to oversee the world's most chaotic family reunion. And that's before the Covenant of St. George launches a full scale strike against the cryptids of Manhattan, followed quickly by an attack on the Campbell Family Carnival.
It's going to take every advantage and every ally they have for the Prices to survive what's coming-and for Mary, to avoid finding out the answer to a question she's never wanted to know: what happens to a babysitting ghost if she loses the people she's promised to protect?