Can the new UN be taken over from the existing UN?  

The existing UN is not dissolvable due to its statute as long as all 5 constant members: the U.S. , Great Britain , France , China or Russia agrees. And as in the new UN the privileges (example right of veto) are omitted, politicians of these countries will set to maintain the existing UN.   

Such a new UN is not realistic, or?

Even if hope is very limited I still see a chance. I see these in humans of all countries, which support this initiative.

How could such an initiative look like? 

The beginning could be done by the pressure of the population, whereas 5-10 countries decide by themselves to cancel their own military and relief organizations in favour of a new joint union.   

Which tasks is to be given to the ethics council?

The ethics council validates all decisions on their future prospects.