I have been fortunate that I have great in-laws and parents, so this kind of thing has never been an issue. I am sorry for you that you have to deal with this loss. And, I say it is a loss, because that's how you should think of it. Their behavior is unacceptable, not helpful to the beginning of a young couple's marriage, and so, in part to protect your wife from them, once this wedding is over (and maybe before if they don't play nicer), you need to cut off contact with them.
If they are indeed mentally unstable, it might be the last you hear from them until they die, but that will be the price you have to pay for you and your wife to have a good life. If they are NOT mentally unstable or they get help, then they can change. You should leave the door open for that possibility of a change, but it must come from them and be initiated by them.
Here's the post-wedding letter I would send them:
"Dear Mom and Dad,
It pains me to have to write this letter to you both, because I love you, but we are going to have to have some time apart. I owe that to [name of wife] because she doesn't deserve this kind of unnecessary conflict; and quite frankly, neither do I.
The constant negativity the two of you had over every detail of our wedding showed me that you didn't realize it wasn't about you. We tried several times to meet with you, but you couldn't make time for that and then got upset that we never visited. That is a no-win game that I will not play.
Now, as a married man, my first allegiance is to [name of wife]. I will protect her and the peacefulness in our marriage at all costs, even if that includes keeping the two of you out of our lives.
This letter is not intended to be an ending, but hopefully a beginning, and it IS an ultimatum. After we have some time away from you and you have time to find a way to change your ways, our interaction with you is dependent upon that change.
The ball is in your court. If down the road you would like to see us, then, assuming we are available, we will gladly accept your invitation. My expectation is that you will be pleasant. I have no room for dysfunction in my life.
Here's hoping we see you soon.
[sign your name]"