Not necessarily. If Jeremy was innocent, it is possible (remotely) that the blood was a mixture of Nevill and June's, and it was possible (fair to say remotely) that Sheila managed to overpower Nevill and shoot her whole family without getting any blood on her hands and feet, and without getting any bullet residue on her hands (or washing) etc .... If this is the case, the only person necessarily lying is Julie Mugford.
How would NB's blood have entered the silencer when he did not even sustain any contact shots? Its unlikely the draw back/back spatter phenomenon would occur with a small calibre firearm and subsonic ammo. Attach a silencer and its even less likely. NB did not even sustain any contact shots and this is part of the mechanism required for draw back to take place: expanding gases from bullet entry force blood and tissue backwards into firearm.
You have missed off the paint/scratches.
The state of Sheila's nightdress, hands and feet and overpowering NB can easily be explained from a defence perspective.
If you look at the part of the judge's summing up here you will see the blood weighed very heavily on the minds of jurors.
Had this crime have been committed in US it would never have seen the inside of a court because the expertise and lay knowledge of firearms is a world away compared to the UK. More so back in the 80's.