Visa for my sister and brother-in-law

[visa410]

Hello,

One of our family friend has sent an invitation letter to my sister and Brother in law to join in the 25th anniversary celebrations of thier church in NY.
I sponsered them previously but got rejected twice. they would like to visit us in May.

Since the church is willing to sponsor them what are the documents that they have to provide us. and what documents we need to take? we would really appreciate ure help. Thanks