Hello Debbie,
It may be the case, perhaps even likely, that the 'proof' you're seeking will not be forthcoming. In these cases, as genealogists we need to make a determination based on an exhaustive search of the available records and the weight of the evidence. Since vital records do not exist for the time period you're seeking, we need to look for substitutes. For Wyszkow, it appears that marriage alegata are available which sometimes include birth or other supplemental records for the parties in the marriage. If you can find those for the people in question, they may provide additional information.
If you haven't already, you should try to locate the death records for these presumed siblings as those may have their parents' names. Sometimes death records of parents will name the children or at least give the number of living children--it appears that Ajzyk died in 1883 and Chaja Sura in 1884 so you should get those records translated if you haven't already.
In cases like these, I've also used Ashkenazic naming traditions to substantiate a theory of shared ancestry. If these presumed siblings all have children or grandchildren with the given names Ajzyk and Chaja Sura, it's likely they were named after shared ancestors. For example, it appears that Abram Josek had a delayed 1898 birth registration for a daughter named Chaja Sura.
Finally, I would suggest contacting the JRI-Poland Town Leader to see if he has any additional information or suggestions . . . I know he has been active on this forum in the past.
Hopefully this helps!
Regards,
Aaron Slotnik
Chicago, IL
