William H. Leas was a lawyer in Des Moines, Polk County, Iowa. He was also elected as Mayor of Des Moines in 1864. The minor children you mention are not living with him according to the 1880 census, for only his wife and son are listed. The names you mention do not relate to any of his inlaws either.
It could be that the "signed guardingship" had something to do with his legal duties as a lawyer, rather then what you suspect.