Our kids can be our harshest critics and appreciate the least what we have done. You can always hold out the silent hope that one day they will realize if you could just get over it, you would have by now. Anyway, there could be a grain of truth in what they say - but even if there is, getting over something is not a matter of willing it to happen.
My loved ones have occasionally said variations on "get over it" to me but I also have a good sense of my own situation and realize not everyone - even from the vantage of being an exJW - feels the same way as me.
All I can recommend is you graciously thank them for their feedback but also acknowledge to yourself that we are all individuals who have been affected in different ways by our connection to the organization. My view is the more devastating impacts we have witnessed and observed in the organization, the harder it is to "get over it". But over time, we might manage better our expectations of others (drop the wish that they will read your book) and respond in healthier ways to your own pain and suffering.