Just a couple of thoughts:
I really liked the idea of doing something special for your husband's memory (like buying the ornament). A friend buys and gives away a balloon each trip in memory of her father. If it's a tradition, then you can feel like you are honoring the memories not fighting them.
And I'd do it early in the trip, so that you can relax afterwards and maybe start a tradition of having one morning where you do something special for or with one daughter and the next morning do something special for or with the other daughter (like buy a pair of disney socks, or take a picture by a Disney icon, or ride the boat from Hollywood Studios to Epcot or make a pin in the community center). Something free or cheap that you can do each year as a little ritual.
Best wishes for a wonderful trip.