Who were Eldad and Meidad?
Targum Yonasan: They were the sons of Elitzafan ben Parnach, 1 to whom Yocheved, Moshe' mother, bore them, after Amram divorced her in Egypt, following the decree to kill all the newborn baby boys, 2 and he married her. 3
Why did they remain in the camp and not go with the other elders to the Ohel Mo'ed?
Rashi (from Sanhedrin, 17a): They were originally chosen to become elders, but they remained in the camp, because they considered themselves unworthy of becoming communal leaders. 1
What did they prophesy?
Rashi (on Pasuk 28): They prophesied that Moshe would die and that Yehoshua, would take Yisrael into Eretz Yisrael.
Targum Yonasan: Eldad prophesied that Moshe would die and that Yehoshua, would take Yisrael into Eretz Yisrael and inherit them the land, Meidad, about the quails and their consequences, 1 and both of them, about Gog and Magog and about Techi'as ha'Mesim. 2
Why were there two elders too many - thereby prompting Eldad and Meidad to stand down?
Rashi: Moshe initially chose 72 elders, six from each tribe, even though he required only 70 elders, 1 and he knew that no tribe would willingly forego one candidate.
Rashi: He therefore took 72 pieces of paper, on 70 of which he wrote 'Zakein', and two of which he left blank, and after placing them in a box, he intended to ask each elder to take one ... - like he did regarding the Bechoros (Refer to 3:50:1:1). Only Eldad and Meidad stood down of their own accord.
What are the implications of "va'Tanach Aleihem ha'Ru'ach"?
Rashi writes that on 72 lots he wrote 'Zaken', and two he left blank; each elder will take one. Still, they will complain. Everyone will want to take first, when all papers of 'Zaken' are there! The latter can say 'presumably, the first will pick 'Zaken', for they are the majority!'
Refer to 3:50:151:1-6.
Rashi writes that on 72 lots he wrote 'Zaken', and two of which he left blank. He could have made lots for the Shevatim (how many Zekenim each will have on the Sanhedrin)
Moshav Zekenim: It is better that members of the Sanhedrin pick for themselves.