OK, so the grandmother of the twins was not involved if that was the case. Could there be female siblings of Shiela who shared the same mother (maternal siblings)?
There were only three adults in the house, Robbity
Two women and one man — Sheila, June and Nevill
Plus two little boys — Daniel and Nicholas
The silencer that Jeremy used and then hid contained the blood of three adults.
Sheila had a rare blood group — A Rhesus negative. The same as one of the blood groups in the silencer. That blood group (A) had 17 out of 20 possible markers which exactly matched Sheila’s. They were unable to pick up the remaining three markers, and as the defence desperately tried to suggest it “may” not have been Sheila’s blood as they hadn’t found all 20 markers, the court was legally bound to say they couldn’t prove 100% that the blood was Sheila’s, despite the forensic scientist saying that 17 markers exactly matching each other meant the chances of it NOT being Sheila’s blood was a trillion to one.
So basically, the blood was Sheila’s. Fact.