You might try the Friends of Allen County resources. I see your grandparents obituaries indexed there. You can request them or if you live near Fort Wayne can go in and look at them in the library.
http://friendsofallencounty.org/results_obits1900.phpI am working on the Sinnigen - or the Sinigen family as well. Helena (Sinigen) Arens was my great great grandmother. She was born in Ashendorf Germany and immigrated to the US - to Fort Wayne, Allen County, IL. From family history we knew that there was a connection with the Sinigen family in Fort Wayne, but naturalization records showed that it was Helena's maiden name.
Her parents were Susanna (Avers) and Henry Sinigen. I believe that both of them immigrated to Fort Wayne as well - or it might have just been Susanna. In any case that was around 1872.
There were still Sinigens that were close family while my grandmother was growing up - Heiny or possibly Henry Sinigen lived with his mother on John Street - this had to be soon after 1930 in Fort Wayne.
The Arens family seems to be very connected to St. Peter's church - not sure if the Sinigen's were Catholic as well - if so there might be information there.
Let me know if you come across info, I'd love to share!