I think the Portuguese police achieved everything they wanted when it turned out in the end that the tapas group were unwilling to cooperate in a child disappearance investigation.
The tapas group had watched elements of the PJ attempt to pin this crime on their innocent friends and had themselves been the victims of character assassination in the media (swingers).
They would have to be insane to trust the motives of the PJ after that.
Anyone who can't see that has no ability to put themselves in someone else's shoes IMO.
IMO the PJ knew they would not attend for obvious reasons. In fact they were banking on it. Hence their instruction not to bring the children and their admission that they could give no guarantees re media presence. All intended to put the tapas off attending IMO.
IMO their decision not to attend was then used as a face-saving operation to explain the shelving of the case. Totally unnecessary IMO as all the PJ had to say was they they had done their best with limited resources and with no officially established directives on this particular crime - but unfortunately had not been able to solve the case thus far.
That would have been an acceptable reason for most people IMO.
AIMHO