Phantom Finders
6 Books Series
Publisher: ABDO
Writer: Brigitte Henry Cooper
Buy it here

Abby and Theo have the coolest family. Rather than gather at barbeques or plan beach vacations, the Winstons investigate the spooky stories and unsolved mysteries of their town, Murky Creek. Grandpa Winston started the tradition, and now he's passing it on to Abby and Theo! When odd goings-on and suspicious happenings plague the citizens of Murky Creek, it's up to the two kids to dig up clues and crack the case before things get any creepier.