If they died in Iowa then you might get copies of their death certificates and these usually list the mortuary and cemetery. Are you sure it was Nebraska that they were buried in? There is an Osceola County in Iowa.

Osceola in Nebraska is in Polk County which is pretty far away from Council Bluffs, IA

Polk County Clerk
Courthouse
Osceola, NE 68651
(402) 747-5431