I think I found the Ellis island entry for the elder Jonas, recorded as Johann Rubkalnis, 52, arrived 8/21/1907, going to Chicago, from town of Alexandrowa. The writing on the manifest is very hard to read. I think it says he is going to a son in law, but I can't make out the name and I'm not sure who is coming from, possibly "woman Marian". But he appears to be traveling alone.
In a book I have about victims of WW2 Soviet terror, there is one listing:
Rupkalvis, Dovas, son of Gretas, born 1911, resided Zemaiciu Naumiestyje, Taurages district, Silutes region, a farmer, sent to a prison camp 1941 06 12, and he died there in 1943. (Note that the location name-endings are spelled according to grammar usage.)
The Lithuanian on-line phone directory has a lisitng of Diteris Rupkalvis in the town of Silutes. You could look at the listing to get the address and try contacting him