@cdn,
CDN it is a shame that there is such bad blood here but from your statements you do have some contact with them and perhaps if you can keep your cool you can just tell them the same thing you had posted here in a very calm manner.
You do not wish to interfere with the child living arrangements but you must be able to see her and if you are not allow to do that you will need to file a missing person report and perhaps even sadder a charge of interfering with child custody against her husband.
Give them a time frame and then if all else fail file such paperwork with the local DA as I can not see how the DA could at that point could refused to get involved.
But the above is the very last thing I would do however.
Side note keep detail records of your phone conversations over this matter. Times and dates and who and what was said. Write it down at once.
In my state recording such conversation without both parties agreeing is illegal so I can not suggest you also record such unless you check first concerning your state laws.
Speaking of the law please take note all the above suggestions is from someone who is not a lawyer and have no training in the law, it just my layman opinions.
There been a few people on this system who had claimed to be lawyers and perhaps one of them will add to the laymen opinions that had been express here to date.
Good luck to all of you in any case.