Sadly, I can’t tell you what is going on with your daughter-in-law without interviewing her. From your description, it is possible that she is suffering from a psychosis related to her pregnancy. It’s rare but it does sometimes happen. The fact that she is accusing multiple people and distrusting people around her who you think are trustworthy suggests that the “abuse” is in her head, but I won’t rule it out. Just because someone is acting symptomatic doesn’t mean that there isn’t also something serious going on.
She needs to be evaluated by a mental health professional, not blamed or shamed or arrested. Since she has other children, it is especially important that she get an evaluation — for their protection as well as hers. Since she reached out to your son to take her other children when she was in such distress (despite the fact that she is accusing him of abusing her), I’m concerned. It may be necessary for him to contact child protective services to ensure the children’s safety. Although I don’t like the term “crazy”, her parents may be correct that there is something seriously wrong.
Since she is attending the church, is it possible that the pastor can influence her to see her obstetrician for a referral to a psychiatrist or psychologist? The pastor may be in a unique position to encourage her to get the help and support she needs. Since psychosis related to pregnancy is rare, the evaluator should be alerted that there is some concern by those close to her that it is a possibility.
As for the wedding bands. Once a gift is given, a receiver can do with it what they wish. Although unfortunate, she does have the right to pawn her own ring. But she doesn’t have the right to demand that your son return the ring she gave him.
I wish you well.