Agree - various steps could be:
No more animosity - sword(s) down - thats all on PH (IMHO).
Able to calmly be in same space when required with no interaction - they did that at their uncles memorial last Aug, also PP funeral, Diana memorial, Jubilee, QE2 funeral, Coronation.
Wishing each other and their children happy birthday in private (this did happen with KC3 - not sure it still does as apparently he was pissed off that PH spoke about his private birthday call with A&L publicly).
Wishing each other and their children happy birthday in public - think milestone birthdays are marked for adults? Not sure about DCs?
PH meeting KC3 in private in UK.
PH meeting KC3 in private in UK with his DCs.
PH meeting PW and PC in private in UK.
PH meeting PW and PC in private in UK with his DCs.
PH seen interacting socially with KC3 in public in UK.
PH seen interacting socially with KC3 and his DCs in public in UK.
PH seen interacting socially with PW and PC in public in UK.
PH and his DCs seen interacting socially with all The Wales in public.
I dont think MM will let her DCs come to the UK (think there is some random royal rule about KC3 having some sort of agency over them?) - also would be a climb down for PH as its 'not safe'.
Suppose there is the option for KC3 to meet his DGC in US or neutral ground in Europe?
But this whole move back into the family house and family business is always nonsense and something no other family fued would consider.