The Missing Page (Page & Sommers, #2) by Cat Sebastian 

In this second book (definitely read Hither, Page first) Dr. James Sommers is summoned to the estate of an uncle who has bequeathed him a paltry item, but more importantly, has gathered together the blood family that has ignored or rejected him for 20 years, since the mysterious disappearance of his cousin Rose.

The uncle’s will stipulates that whoever can find out the true whereabouts of Rose will inherit the estate. Not that James wants the estate, he’s happy with his found family and his job, but a kindly relative will be ousted from the only home she’s ever known if the estate goes elsewhere, so James starts investigating.

Luckily, Leo has just finished a job and he drives down to help the investigation, and for him and James to begin figuring out what it means that leo’s clothes now hang in James’ closet and that James loves having him come to his house when Leo finishes a job.

This is super sweet, focusing on found family relationships and a cozy mystery about the disappeared Rose. More non-conventional relationships in a historical context.