Madara can't really be expected to overcome flying thunder god when even Tobi and the nine tails couldn't do anything. Minato sacrificed himself in order to preserve the life of a helpless newborn, his heroism was his only drawback. Without newborn Naruto around, nothing is stopping Minato from tagging Madara (like when Minato tagged Tobi, or the 8 tails with flying thunder god). Minato wins without Kushina. :/ Add the 9 tails jinchuriki as his backup and he's pretty overpowered, even for Madara.
I think Susanoo and wood clones as well as deva path can
1st, not allow anyone of them to hit him
2. even if tagged it'd be a wood clone that'd be killed, and Madara can make a lot more than Minato and Kushina have chakra to overcome.
3. remove all the kunai's from the area
let's also not forget that Madara is quite quick himself too, for example when he just simply kills couple ninjas with just a sword.
Minato's rasengan wouldn't do much harm either to susanoo, wood protection (sounds so weird xD) or Madara himself. Let's not forget that having hashirama implanted is quite a big of a deal here.
Minato and Kushina vs madara is like saying "ok so.. So6P vs. any character backed up by fanboys". Because Madara is almost like a Rikkudou. Only thing he's lacking to be exactly like him is Ying Yang Mastery and Ten tails' chakra (though his chakra is already extraordinary and exceptionally dark and powerful)