It looked like Jonjo's parents had been shown down there, either for formal ID purposes or just to say goodbye, so that didn't strike me as implausible at all. Implausible is the restriction of the DNA to ages 18-44 when so many key players are probably below that (the sixth formers) or older (Alan, Petrie, but apparently not Marr!)
Dessie's mum was the one Annie set up with Leighton in the first ep, and it was implied she decided to go on a (another?) date with him after all.
I'm wondering if Keiran was blackmailing Niall Swift over shagging Dessie? He's way too quiet. Did like how Evie seemed to be growing up in ep5 though.