The wedding in in the Oakland Hills, so we are suggesting people fly into Oakland airport (OAK).
You might be able to fly into San Francisco airport cheaper if you find a deal and there may be more non-stop flight options.
Example: I checked for flights IND–>OAK and IND–>SFO on the same days.
The results on Southwest? $300 one way to OAK, $161 one way to SFO. So that is a big difference!
Delta usually has non-stop flights from Detroit to SFO.