Are they supposed to be
Ethnically Russian, or Russian Jewish Humans?

No.

Worf didn't have human parents. How could a full-blooded Klingon have human parents? Illogical! Does not compute! So your question is moot.

He did, however, have human foster parents, who I believe were Russian Naturists... but not Jewish.

Russian Naturists? Where did you get that from? Yes, they lived on the "farm world of Gault" but Sergey was also an enlisted man in Starfleet.

Didn't you see them walking around naked on the Enterprise? J

Possibly Sarcasm meant Russian nationals, but that doesn't quite make sense either, given that Earth is unified.

Don't put too much thought in it, guys... I just wanted to demonstrate to Anonymous that he's not the only one who can make innane posts.

Worf's parents have, naturally stayed clothed.

The actress who played Helena died in the mid-'90's, so that's why we did not see her or Sergey at Worf and Jadzia's wedding.

But what about Nikolai? Would he have been contacted somehow about his foster brother getting married, or was he too involved in his new life with the Boraalans?

And Paul Sorvino could easily have made a guest appearance on DS9, even though at that time he was in a CBS show called "That's Life".

Just thought I would add this: the version of "That's Life" that Paul Sorvino was on was a drama, it debuted on CBS in 2000 and lasted two years. Apparently there was *another* show with the same title on ABC two years earlier, but it was a sitcom that was cancelled after five episodes. The Catholic League for Religious & Civil Rights denounced it immediately and called it "the most anti-Catholic TV show ever."

Live and learn. One was a heartwarming drama, the other was an offensive (and some would say blasphemous) sitcom that was on two years before the other one.

And I still wish that Paul Sorvino had guest-starred as Nikolai in that episode!