Unless you have to have NW, I would go with UA for sure. They will give you the lowest fare available and also will allow you to change it if you need to for no extra charges. I would say UA is the best for these type of fares. I had to use one this year and they came out like a champ. Just have the Dr. information or the funeral homes information.
They did very well for me and I'm sure you will see they will do the same for you. The fact they allow you to change the flights with no extra costs is a plus also for us. I had to stay an extra couple days to clean up some issues and they changed the return with no problem at all.
Give them a call.