To feel constrained as to the proper response to Meghan and Harry by concern that "we can't do that, because then they'll tell this lie" or "we can't do this because then they'll tell that lie" is to give in to blackmail and that is never a solution.
In my opinion, they both suffer from severe mental disorder and the Royal Family quite rightly does not bow to pressure to discuss this in public. On the other hand, the manifestation of their mental derangement is in large part a desire for vengeance for perceived slights and a willingness to lie to attack the monarchy and the fabric of British society. However, unlike any ordinary family dispute, they do this from a position of British royal status. That cannot be allowed to continue - the family squabbles and the constitutional threat must be addressed as two separate matters.
I am only concerned with the constitutional side of this equation. I believe that they will never be silenced. That is the nature of their psychiatric problems. They must therefore be marginalised. The majority of the British people disagree with those who assert that the monarchy has no purpose. The monarchy has a crucial role which is relevant to everyday life in the UK. The monarchy stands to protect our constitution, uphold our values (including integrity, free speech, fairness and natural justice) and act as the glue which binds us together within the UK and with the people of the Commonwealth, presenting our best face to the world and facilitating shared problem solving and mutual support. To fulfil that role in the service of the British people and the Commonwealth, I believe that anyone having royal status must observe certain constraints. By their own admission, Harry and Meghan hold the monarchy in disdain and pour scorn on the inherent and essential constraints. They will not and cannot fulfil the role and therefore cannot hold royal status. The Queen, with the assistance of Parliament as necessary, should therefore remove all royal status - titles, place in the succession (including Harry and his offspring), and any continuing funding from the privy purse.
No doubt the family will then try to explore in private the scope for forgiveness, as Michelle Obama seems to suggest. If the Royal Family has any sense, they will be doing this with extreme caution and under the guidance of mental health professionals who can guide them on effective communication with malignant narcissists and how to minimise further damage to their own well-being in the compassionate attempt.
The same principles are equally applicable to any other member of the Royal Family who wishes to opt out of the obligations and constraints inherent in the role.