Visitor visa for uncle and aunty

[chary]

I would like to invite my uncle (my monther-in-law's brother) and his wife to visit US for 3 months. I am on H-1B and my wife is on H-4 (house wife) and we have two kids. My uncle has big business and properties in Bombay and have two young sons.
My question is;
1. Who should be the sponserer? Me or my wife?
2. Who should make the affidavit and write the invitation letter?

Please assist asap.

[immihelp]

1 & 2. You.