This side of the Dalling family is only distantly related to my family, so is on the fringe of my tree.
So I am not sure who Walter Dalling is or where he fits.
I suspect Thursa and Luana are sisters and by 1871 their parents are deceased, hence living with Walter,
Saying they are his daughters and he is widowed to the census saves a lot of questions from the authorities.
Also, in 1871 Thursa is about 26 years, not 19 as given.