You appear to be suggesting that 2 parallel rwys north of the airport should not be built simply because taxiing aircraft would have to cross live rwys. Is this correct?
No, I'm suggesting that the number of runway crossings resulting from two new runways north of the existing ones and which are also used by T1/T2/T3/T5 traffic would be
significantly higher than at present. That's the issue.
But it's all rather irrelevant now that we have seen Heathrow's proposals which, strangely, don't include your 2 northern runway option.