In looking for possible connections I found Conrad and Mary.I wondered if Mary was a second marriage for Conrad as Joseph was born app 1813.Interestingly Joseph was also a tailor and that was so common for father and son to have the same profession.
Another name that always looks promising is Jacob Eberhart.Do you know if these men, who lived near each other at that time, were brothers?
Another question....I have been thinking of trying church records.Do you have a church affiliation for Conrad?I was considering going through the Lutheran churcheswith published records and seeing if any Eberharts turn up.
I have not had much luck connecting Joseph since I found the last name of Eliza.With Mahanna not being very common it hasn't helped me very much.
I do know the family is related to the Vogelgesangs who descended from Jacob Vogelgesang.Joseph and Eliza's daughter Catherine married a Vogelgesang.I don't know if your husband is aware of this being a name in his family.If so it could be a help in connecting the Eberharts.
Sorry I could not be of more help.I do suspect Conrad and Joseph are related.But so far it has only been a suspicion.