I just had a quick look at some Lithuanian surname sites.
Looks like the name is (commonly) spelt Vosylius in Lithuanian:
https://lietuvai.lt/wiki/Vosylius_(reik%C5%A1m%C4%97s)
This site
https://www.myheritage.lt/FP/genealogy-welcome.php?s=210490491 claims that it's basically a Lithuanianized form of the given name Vasiliy. Quote: "According to one of the versions, the Vosylius family originates from the Marijampolė area. In old documents the surname is written as Vasilius; by the way, there were also various distortions (Vasylius; Vosilius, even Vasiulis). It is likely that the origin of the surname is Russian, e.g. In "History of Lithuania" by A. Šapoka, Duke Vasilij of Moscow, who married Vytautas' daughter Sofija, is Lithuanianized as Vosylius."
Now, like I said, I only did a very superficial search, so I'm not sure how accurate or reliable this source is. Linguistically speaking, their claim does make sense, though.
As for the Wosilius spelling: I'd assume this might be a Polonization of the name. Bear in mind that Poland and Lithuania were once "united" in the Polish–Lithuanian Commonwealth:
https://en.wikipedia.org/wiki/Polish%E2%80%93Lithuanian_CommonwealthPlus, Marijampolė borders Poland:
https://en.wikipedia.org/wiki/Marijampol%C4%97
Are you sure his given name was spelt Yonus? Jonas is the most common Lithuanian form of John, but there is also Jonius (
https://www.tevu-darzelis.lt/vaiku-vardai/jonius/). In any case, it looks like he simply Anglicized his given name.
(Edit: Typo)
This message was edited 9/29/2022, 8:54 AM