Why would Mi6 kill 2 children, why would Mi6 go to the trouble of framing Sheila, surely if they wanted Bamber as well it would have been planned better, don't forget who the Lawyer was who made these claims Giovanni De Stefano.
With respect you completely mis understand the Mi6 theory.
NO ONE including Bamber or De Stefano has ever said Mi6 were involved in the murders.
And of course Mi6 do not murder children or frame people.
The theory is that June and probably Neville were themselves ex Mi6.
An "enemy" of Mi6 then killed them as revenge for the work they did on behalf of Mi6.
And they are one of 5 such ex Mi6 officers to be killed in similar circumstances.
De Stefano whilst Bambers lawyer stated that he was approached by an ex SAS soldier.
Mi6 and SAS work very closely together.
This SAS guy told Stefano that he knew that there were 5 related cases of murders of ex MI6 officers and that the Bambers were one of the cases.
If an ex SAS guy did actually say this then it would very likely be true.
The only question is whether De Stefano is lying or not about being approached by this SAS guy.
De Stefano's credibility in general is in doubt because of his own prison sentence.