It sounds like things have gotten very heated. So, first of all, I suggest you avoid any further interaction until you have a chance to learn what your next steps need to be. You definitely want to be perceived as the "good guys," especially if this does have to go to court, where your adversary will come armed with all your communications and actions to paint you as "bad guys."
Immediately, as in as soon as you're done reading this, you need to get in touch with your partner's broker and make them aware of this matter. It's the broker's job to advise agents how to handle sticky situations, and even to get directly involved. A good broker will put a prompt smackdown on anyone (especially older, more experienced agents) hassling their newer agents. If your partner is very "new" to real estate, they may have discovered yet how to utilize their broker for exactly this type of thing. I'm very surprised the broker didn't go kick some fanny over that $10,000 discrepancy! That would never have gotten by mine!
ASAP, speak with the attorney who represented you in this transaction. If you didn't have an attorney, place a call to a local real estate attorney. Must be local in YOUR market, and must specialize in real estate so that you're sure they know all the ins and outs of local real estate law. Attorneys are usually willing to give someone a quick phone consult (especially when vulnerable people get bullied).
Once you have a clear path forward and know exactly what you need to do, THEN reengage with your adversaries but keep your communications short and formal, and only those required by legal process. No more long emails!
So sorry you're going through this. Best of luck. Start with the broker.