He started off (I thought) by hinting that 'May' might not have been a full sister. So why didn't they get a birth certificate or the baptism (if baptised) to confirm her parentage - and for Roach's mother and other aunt?
Well, obviously, they will have done, and I presume as it wasn't mentioned that they were all legitimate and full, not half sisters, or adopted, or something - and to mention that would have removed the air of mystery.
With the name Waddicor, I could've told them at the start that they were very likely connected to Darwen. It seemed that they were about to start talking about Darwen, but then suddenly changed their minds.