Thanks for the added info to your first message.
There is a couple of things that stand out to me:
1) Searching the archives of the Netherlands there is no indication of the parents of Peter, John and "Doras". Diedrich is decidedly more of a German first name than a Dutch name. And, I could not find one "Gergen" family in the Netherlands search site that covers all of the Netherlands. The surname of "Gergen" is, like Diedrich, a very un-Dutch surname.
2) That leads me to my next observation: On the 1860 and 1870 census records, Peter states he is Dutch. On the 1880 and 1900 census records he states he is German. Now the surname "Mares" can be found in the Netherlands, almost exclusively in the province of Limburg, near the Belgium border. But, it is also a very German surname. Could it be that the brothers came from Germany and not the Netherlands?
3) There is no town/city name of Stockton in the Netherlands. Not even close. If they were born in the Netherlands then maybe the transcriber writing their birthplace did so phonetically which happened frequently. In whatever case the error ocurred there is 100% surety that no such place exists in the Netherlands.
4) One thing that caught my eye was the name of the younger brother of Peter and John, "Doras". In the province of Limburg, the Netherlands, there was a prominent "Mares" family who had in its line males with the first name of "Joris". Could "Doras" actually be "Joris"?
5) The last name "Mares" was also spelled "Marres", "Meres", and "Marez". There were probably a few more spellings throughout time so keep that in mind when doing your research.
6) I would obtain (if you have not already done so) the Naturalization papers for Peter Mares. It was recorded in the Waupaca Circuit Court on 17 October 1892 in Volume 1, page 468 of the Naturalizations book. Maybe that would shed some light on Peter's place of birth and what ship he came to America on.
7) Post under the Netherlands board (General Board and province of Limburg Board) on Rootsweb and see if there will be some help from others, especially those researchers that are in the Netherlands. They probably know other search sites that may be of help.
I will keep checking some additional sources to see if the question about Peter and his brothers can be answered.