Using Face ID to approve family purchases is expected in iOS 11.3 but it's still in beta so there's still no guarantee. You can also disable the option to call emergency services within the settings if you don't want that feature turned on. I haven't had any issues with taking inadvertent screenshots even though I keep mine in my pocket as well.
All-in-all, if you're unhappy then return it and get something that suits your needs and will make you happy. There's no reason holding on to such an expensive device if you aren't happy with it.