I was referring to your great grandfather with court suggestion. I doubt there is a Federal District Court in Salem. It probably would be in Boston. They should have some paperwork on him if he was anywhere in Mass. If he served during WWI, he would gain citizenship through the military and this would be in Washington Federal Court. This was the easiest way to get naturalized. Your great grandmother would not have applied for citizenship until after sufferage, and only then if she wanted to vote, OR after the 1940's if she applied for Social Security.
If the church in Salem burned, there might be copies in the cathedral for the archdioceses.
If you don't know where your grandfather was baptized, check the church where he was married. The wedding church would have to write to the baptismal church to confirm the baptism. And again, your grandfather's baptismal records should have the parent's place of birth. With this info, you can check the LDS (Church of Latter Day Saints) microfilms of the Polish church for your great grandparents baptisms and marriage. Considering the time frame and depending on where in Poland this took place, you probably do not need Polish as the records were probably recorded in Latin, German or Cyrillic. If they were in the German partition, there would be at least 4 copies, two at the church (one in German and one in Polish, one at the local government office and one in Berlin. If they were in the Russian partition, these are the toughest because it's in Cyrillic and even modern Russians don't read Cyrillic. In the Austrian partition, the records could be in either Latin or Polish.
You mentioned they were separated. After the end of WWI, some Poles went back, so you might also check to see if a Passport was issued to him. His occupation might also give some indication of what happened to him. If he was a fisherman, he could be lost at sea. If he worked on the railroads and died, they just buried those workers along the tracks. If he was in the Penn. coal mines, getting records can be tough because you need the exact spelling of the name he used to get anything, and many poles used a variety of name spellings.