According to Professor Ephraim Orbach in his seminal book “Ba’alei Hatosafot”, pages 615-616, the Tosfot on Eiruvin were probably compiled in the middle 1300s, by a talmid of Rav Yitchok of Tresson, who was a talmid of Rabeinu Peretz and the Rosh. Another possibility is Rav Yitzchok of Keinon (sp.?). Prof. Orbach mentions curious possible references to the Black Plague (21: d”h amru) , which began in 1348.
According to Grossman in his “Chachmei Ashkenaz Harishonim”, Rashi on Ta’anit is still a mystery. There was a claim that a ktav yad was found in Spain, but no proof that it was Rashi’s, nor do we have this ktav yad. The consensus for now is that it was written by “chachmei Magentza”, a loosely defined group in Magentza (Mainz)in the eleventh century, who were the predecessors and teachers of Rashi.