1.Look the chapter when Minato fights against Tobi.. you'll see that Tobi clearly does a summoning jutsu.. and summons the nine tails. Tobi, in that chapter, has a contract with the kyubi, just after making a genjutsu on him with the sharingan. I'm not lying just saying what happens in that chapter.
2.Tobi is controlling the jinchuriki, yes, being able to make that these jinchuriki, who hadn't controlled their tailed beasts except of Yagura (danzoo said: we know that there have been only 4 people who have been able to control a tailed beast: yagura, killer bee, hashirama senju and uchiha madara), making appear in their full beast mode. Controlling them just with a sharingan (genjutsu), and the power of the rinnegan.. Sorry but I think this is controlling a tailed beast. Obviously, he has some problems, because he is controlling 6 tailed beast, but he's been able to control, until now, one or two bijuus for a few time; while he's controlling 5 or 4 jinchurikis more.. Almost nothing.
3. As you know, Tobi is not overpowered now. He isn't able to do any jutsu, except of the jutsu's related to his eyes (space-time ninjutsu, genjutsu, rinnegan techniques..). That he needs help to obtain the bijuus is out of question. The most of them ara extremely protected by their villages. Plus, if a only person started to kill all the jinchurikis of all the villages it's obvious that people would have started to have fear of him. And that's not between his interests because he wanted, until the war, to be in the anonymatous. (Sorry for my english..)