I owned BMWs almost exclusively before I had kids. I wouldn't go any smaller than a 5 series, but even so, a sedan with 2 car seats is not only back-breaking (nothing like lifting a sleeping toddler out of a ground-level vehicle), but a tight squeeze. My husband and I are both tall, and there's actually plenty of legroom in the front (Germans are tall people, and design their cars accordingly). We considered an X5, but ultimately decided against it because the trunk space was TINY! Have you ever tried to put a stroller in there? Nearly impossible, unless you plan to only ever use an umbrella stroller (and god help you if you also want to put groceries or anything else back there at the same time!).
We ended up getting a Ford Expedition with all the bells and whistles. Love it. Even driving on snow/ice, in the rain, etc, it feels very solid. Plenty of room for strollers, luggage, etc, and now that we are at the age where the kids have carpools to sports, I can fit 6 kids (some of them still in booster seats) no problem, including ALL their stuff. If you want higher-end, you could always go with the Lincoln Navigator (same as the Expedition, really).
But given that you aren't quite there yet, what about a smaller SUV? Lexus makes a nice smaller SUV/crossover. My parents drive one and love it. My concern would be that I'm not sure it would be big enough for your fiance. I'm tall and I feel like there are some blind spots in it due to my height that shorter drivers don't experience. Going with a larger SUV might help with that.