I read this before I went back to bed after getting up at 4am to shovel snow.
I couldn't stop thinking about it.
I really believe that haunted houses are possible. I also think that your daughter really can see them, but she will grow out of that soon, and probably won't remember unless you keep reminding her.
I'm not sure I believe the explanation about the boys running up and down the stairs though, because unless they died there as little boys, their spirits would be grown up and would be where ever their lives took them.
The phsyic could have done the same research that you did too. I haven't decided how I feel about phsyic's yet.
What I wonder about is, what is keeping them there and why haven't they moved on.
My grandparents died in the home I grew up in. It was a violent death and things wheren't quite right in their lives, we heard my grandpa yell at my aunt (she was mental retarded and lived with them until she came to live with us a few months before they died) Heard foot steps, seen shadows of a woman walk across the window etc.
All very strange.