Tobi and Madara have connection. Madara obtained Hashirama's power during their fight and when he died, Tobi proceeded his plans. Even though, Tobi betrayed Madara.
1) That's what i was thinking too,
because how awake the Rinnegan is not confirmed Madara said he awaken it after he dies shortly. 1 tomoe -> 2 tomoe -> 3 tomoe -> MS -> EMS ->
Rinnegan
(This is possible as according to the manga the Uchiha is a cursed clan so maybe their power is lowered in to Sharingans instead of the original Rinnegan , probably one of the SO6P's son did something wrong then therefore is cursed as the son that inherit the ocular power believe power is essential to achieve peace, i believe he did smth wrong like extermination.
2) Some say you need the Senju+Uchiha to awake it.
BUT.. If they really obtain the power of Hashirama then choice 1) will not work.