Help! My crazy inlaws are holding my wife's birth certificate and refuse to let her have it . 1. Is this legal? 2. Is there anything they could do with it as far as identify theft or something similar?

Long story short, my wife's parents are crazy. We've been on pretty rocky terms for a while, for a (supposedly) long list of grievances we've done against them (though they won't tell us what). They refuse to give us any of my wife's possessions, including her birth certificate.

I realize that she can request a birth certificate from her birth state, but we have a concern.

1. They have recently run into money issues, and have joined some cult-like group. They are also currently involved in some sort of health pill scam, and we're concerned that their reluctance to give this up might be more than just bitterness. Would it be possible to do some sort of identify theft using a birth certificate?

2. If we should be concerned about this, is there legal action we can take? Is it even legal for them to withhold this from my wife?

Thanks for your help!