I'm assuming you mean Otto and Mary who lived in Pittsburgh (based solely on the ages you gave).
They appear in the 1900, 1910 and 1920 census records. Otto was born April 1867 in Germany. Mary was born Dec 1867 in Germany. He immigrated ca1880 and she ca1885. They were married ca1890 (although they list a son Marx or Max born in Oct 1889). As a warning they appear in the 1900 census under the spelling with cks on the end rather than chs. No I am not making it up. In German ch at the end of a word has a K sound. Apparently the enumerator spelled it the way it sounded (it doesn't have the same meaning in German that it does in English).
Some of these records you can look at for free at labs.familysearch.org and Ancestry.com. For those you cannot see for free I suggest checking with your local libraries to see if they have Ancestry or Heritage Quest.
To find Mary's maiden you could try getting her death certificate or her obituary. The same is true of any of her children. Assuming they got married in Pittsburgh their marriage record would be on record at the Allegheny County Register of Wills.
The Western Pennsylvania Genealogical Society and the Historical Society of Western Pennsylvania (both in Pittsburgh) might be able to help you find their obits which should list children's names if nothing else.