I'm a novice, a student with low hours.
But experienced with in laws...
A couple of points come to mind. First, you say you talk flying with him a lot, has he said things that indicate he has disdain for GA flying, private pilots? Does he seem to like you otherwise?
I'm thinking like arnoha that he was out of line with his actions, comments and follow ups trying to sow dissent between you and your wife. You could, totally up to you, give him the benefit of the doubt and allow that he maybe is over protective of his daughter and truly was worried and scared for her safety. That he reacted badly, but out of fear. If you decided to go that route, the only thing I would think might (or not) help, is in order to keep peace, sit down with him, and the weather charts and reports, and go over your evaluation with him. Let him know you had alternate routes picked out in case, and you had a good plan if it turned out the weather was worse than projected/reported. Ask him to point out where he thinks you were taking unreasonable risk.
And it cannot be just "because it could have been worse" as that is always the case isn't it? But it would require being humble, yet projecting that you honestly used best judgement, yet are open to new knowledge if he wants to share exactly why he thinks that flight was so risky. Also that you would never put your wife, or even yourself in a dangerous situation and you did your due diligence and made a decision.
The another alternative I can think of, is talking with your wife and letting her know that he is just wrong, and that she has to let him know she trusts your judgement, and that his comments are not wanted.
Third alternative, let it go, and simply do not keep him in the loop on future flight plans.