Jiraiya, Oro and Tsunade's surnames aren't revealed because of the
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Kishi based the characters on. That's just what their names are. Besides, there are loads of other characters lacking surnames in Narutoverse that are from Konoha. Udon, Moegi, Shizune, Ebisu, Tenten, Shiho, Rin and so on.
I don't get what you mean by Oro's proof but I'm guessing that the word
senjutsu confused you a little.
Senjutsu has nothing to do with the
Senju clan.
The kanji for
Sen in
Senjutsu is
仙 and it literally means
sage, hermit.
The kanji for
Sen in
Senju, on the other hand, is
千 and is the kanji for
the number 1000.