Heart

By a very long way your marriage is far, far more important than your relationship with your brother in law and your husband's relationship with you is far more important than his relationship with his brother. Your husband needs to understand this. 

I have been married to the same woman for over 30 years. In the entirety of that time, I have spent exactly 0 seconds worried that she is going to commit adultery. It simply has never even come up, in any context. We have discussed the intellectual possibility of infidelity, of course. But I don't worry about that for a single moment. She is faithful, and I'm comfortable in that. I cannot speak for her and say whether or not she has worried about such things, but I know myself. For all my numerous imperfections, I know better than to have sex with someone who is not my wife. I spend little more time worrying about my own fidelity than I do my wife's.
Decide deep down in the core of your soul that you will be a faithful partner in marriage. Then marry someone who has that same belief. Voilà! Problem permanently solved.

Motivation is probably the major driver.  And yes, that can, at times, be difficult to discern.  But an abuser's motivation is for control.  Not just controlling an outcome, but specifically for the thrill of having control over another person's life, decisions, and mental state.  A woman who "henpecks" her husband to take out the trash, or paint a room that he's be saying he will paint for six months is not an abuser. She just wants something done. Very likely, a woman who self-deprecatingly jokes about her henpecking is not an abuser, because she can recognize that her behavior is potentially problematic. Abusers generally do not see any problem with their behavior.
To directly answer your question, true abuse from women is rare.  It happens, but is nowhere near as prevalent as is abuse coming from men.
Below, I'm including a letter that was sent to bishops in my area from the regional LDS Family Services representative.  It's a good read for understanding how abusive relationships work. I've redacted the name of the author, as she hasn't exactly consented to having her name plastered on the internet.  If you're genuinely interested, I have a PDF I can forward.