It's a very complex question, with a many parted answer. Let me take a crack.

1. If it's a family emergency, depending on severity, does one airline offer more convenient times and connections over the other? With KL/NW, you face the possibility of more connections, three, as opposed to two, because of KL/NW's AMS hub. If you can get on a nonstop NW flight from FRA, the number connections on both choices of carriers would be equal.

2. I would rate UA, monetarily, in terms of what you can afford. Is the 1200 bucks going to put a hamper on your finances? Can you afford it? I'm guessing yes, because you are raising the comparison. But, if you'd rather have the residual 700 clams by flying KL/NW, go with them.

3. UA transatlantic Y service/hard product is absolutely dreadful. E+ does make it much more bearable, and, yes, I know that many who swear by E+ as the only left that UA does right. I like KLM's transatlantic service in Y quite a bit - they'll feed you well, and there's comp booze, and even a snack cart during the flight (!). If you can score an exit row with them the long flight will be fine.

4. Personally, I'm a miles and points guy, and will, at times, pay more to fly UA (shocking, isn't it) or its partners. Again, you have to measure the worth of 1P to you. Will you have other opportunities in the year to make 1P more cheaply? To put 7000 miles, or so, on an NW/KL account, will that add any worth to said account? Or, will those miles simply be sitting around?

Sorry if that's jumbled or disorganized in any way, just my musings and thoughts. Good luck on the decision, and hope all is okay with your fam.