@butterfly123 Keep in mind, they are both 14 and trying to learn how to navigate these tricky interpersonal relationships. I'm 44 now and I occasionally cringe at some of my behaviors when I first started dating around 16/17, and some of the behaviors I tolerated. Hell, I occasionally cringe at some of the stuff I did and tolerated up to the time I met my now wife almost a decade ago. What I'm truly thankful for (all instances) is that my mother didn't get involved.
My advice to you, unless his behavior towards your daughter rises from stupid to abusive, leave his parents out of it. Instead, be a safe space for your daughter to come to talk and get what's on her mind out. Remind her that her boundaries and expectations are not only valid, but something she should never be afraid to enforce. Remind her that she never needs to tolerate bad behavior just to keep someone in her life. Remind her that she will never be upset about remaining true to herself, but one of the worst feelings is looking back and knowing you compromised on something important.
They're 14, keep supervising them. Keep providing a safe space for her. Remind her that she never has to tolerate anything in her relationships (any of them) that she doesn't want to. Also let her know that she never needs a "reason" to end something with someone else. It's perfectly OK, no matter the relationship (platonic, romantic, professional), for a relationship to run its course. No one is the bad guy, it's just done. In the same vein, remind her that people will treat her the way that she allows, and that a first time someone wrongs her might be chalked up to bad judgement or a mistake, but if it happens a second and third time, that is who the person is, and she should never be afraid to cut someone out of her life whether the first, second, or third time (never let it get beyond three is what I'd tell her). At the end of the day, the most important person she needs to love is herself, after all sometimes it's better to be alone than in bad company.
At the end of the day, these are lessons for her life. It's important for her to learn them while the stakes are relatively low so that when she moves into adulthood. Sometimes the best way to learn these lessons is to live them, and it's pretty tough to live them if parents are swooping in and inserting themselves where they aren't necessarily needed.
Good luck!