The correct answer to this open question is the following.
Although there are no options attached, we can say the following.
The religious group was appointed by President Grant to work with the American Indians and the reason why they were chosen was the following.
US President Ulysses Grant appointed Protestant religious groups such as the Methodists, the Episcopalians, Presbyterians, Baptists, and even Catholic groups to establish his Peace Policy. That was the reason.
It was a time in American history where differences and conflicts characterized the relationship between Native American Indian tribes and teh US federal government.
Ulysses Grant had the will to establish a decent peace policy with the Native Indians and these religious groups were important to them to help Indians integrate into the American culture more decently.