I am not a relative though I do have Jones connections in Dubuque, Iowa
Iowa vital records geenrally don't begin until 1880. Even then they may be sparse or provide little new information. Your best bet is to locate these families in the many online census records available. Once located local records may be examined to find fates and biographical information. It can be a laborious process especially when working on a name like Jones.
Be sure to post queries to message boards for both surnames of interest and locations of interest. They may not be online but you may wsih for local lookups by genealogy societies working in locations where your family lived.
The following from the largest free site(Familysearch.org) gives an approximate birth date for David and Mary which can help distinguish them form people with the same name.
United States Census, 1850 for Emma Jones
Residence:Dubuque county, Dubuque, Iowa
Calculated Birth Year:1846
Digital GS Number:4181031
Dwelling House Number:1832
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