Let's face it, the McCanns have attempted to understate their own culpability from the beginning. The hastily put together story about the child checking was just the beginning. They knew from those first hours that they were going to be criticised and by their own parents. The refusal to answer questions is a recurring theme with them, remember those interviews which Gerry walked out on?
The only interview I know of that Gerry walked out of was the one where although it was made clear beforehand that they were not allowed to discuss the case as that would be breaking the secrecy laws - the first thing the interviewer did was ask questions about the case.
IIRC Gerry pointed that out as he wearily left the room.
As for the 48 questions - have you ever read them? IMO Amaral and co had already decided Kate was guilty and now they needed to come up with a motive - and that was the main aim of that interview.
Questions like the following are a clue to the direction they were going in IMO. Especially question No. 41.
39. Are the twins difficult to get to sleep? Are they restless and does that cause you uneasiness?
40. Is it true that sometimes you despaired with your children’s behaviour and that left you feeling very uneasy?
41. Is it true that in England you even considered handing over Madeleine’s custody to a relative?