Cognac-what are you hoping as an outcome of your communication w/dad? Are you hoping that he will re-think his stand and address your questions? Are you hoping to make HIM think about the behavior and compare it with what a christian is supposed to be like?
I think your sentiments are honest and respectful, the only feedback I might be able to give is maybe be more specific in your outline to him: When I said "......" (put in specifically what your questions were) the family responded by saying "......" (what did they specifically say/do?) I would refrain from leaving anything without definition since your dad may be defensive and defensive people downplay their own actions/or the actions they are trying to defend.
I would eliminate any possibility for him to put his own spin on what happened; list the facts and then how those facts made you feel-(which you did a great job with). Hope this is a helpful comment-good luck.