Why is my Android merging two of my sync'd gmail contacts into one?

[AC Question]

I have a Sony Xperia Z3 Compact with Android 5.0.2. My Wife's and Son's contacts are merged into one (wife's name with son's photo - with all email and phone details contained in the one contact). They are not merged when I look at the contacts list in gmail in my browser and they share no common phone numbers or email addresses.

They used to be linked in a google+ profile but I deleted that profile and neither currently have google+ profiles.