Sorry but I can't make head nor tail of your reasoning here Stephen. What exactly are you saying the Tapas 7 agreed to do and why?
If, as you think, Madeleine died in the apartment, then the rest of the group would have no more responsibility for that - than any other holidaymakers on that complex. They wouldn't need to do thing.
It can't be that they didn't want the police to know about their childcare arrangements - because that's the first thing they told the police. In fact they even wrote the details down and handed it to them.
So if it wasn't that - then what was their reason for agreeing to put themselves at risk of being jailed for perjury, perverting the course of justice, and aiding and abetting the disposal of a child's body? You must have a reason Stephen.
And where does Mrs. Webster come into all this? She had no-one to be responsible for except herself - so why would she agree to take part in a heinous crime, and risk ending up in a jail in a foreign country in her 60's, where she didn't speak the language - and with her husband thousands of miles away in the UK. She hardly knew the McCanns. And do you really think her daughter would allow her own mother - a grandmother, to put herself in such terrible danger?
Anyone who believes that is living in cloud cuckoo land IMO.