Minato and Kushina CAN be revived if...

[yondaime4]

i think the fact that it didnt work and oro had years to figure it out makes me think its possible
and almost likely that he broke into the reaper.

as for the coffin i think the logical response is that oro brought minatos body back but the soul was not present, and he didnt actually try to awaken minato until on the battlefield so oro didnt know the body was without soul. i have wondered this myself and im sure the answers will come up soon enough

 

[TurrinB]

We were directly told Minato couldn't be revived by Edo Tensei since his soul was sealed in Shikka Fuujin.

 

[B00m]

Yeah its because his soul is was sealed

We all know that. I think what the OP is trying to say though is Oro didn't perform the Edo Tensei ritual itself (having sacrifices, etc.), but spawn COFFINS which signifies he already performed the jutsu/sacrificial part and has them at his disposal, which leaves you to question/assume he successfully did the sacrifice part, but spawning it at that moment couldn't happen. I haven't read it in awhile, does the coffin go back down naturally or does Hiruzen cause it to go down because he finally realizes what they are?

Could the 4th not be spawned because part of him was still in Naruto essentially?

 

[shofneb]

Ok I've watched this recently. The Third claims that he stopped the fourth's coffin from rising up because he hit it with some Shurikin. HOWEVER, it was later stated by Kabuto that the reason the fourth could not be revived was because his soul was not in the afterlife. He stated that oroochimaru tried to revive him but failed because of this reason. The third actually did nothing to stop the resurrection.

 

[Kiiszame]

Not a lot is known about the reaper death seal and the edo tensei. For all we know they can be revived but at what cost? Who knows

 

[Xaviour]

Ok I've watched this recently. The Third claims that he stopped the fourth's coffin from rising up because he hit it with some Shurikin. HOWEVER, it was later stated by Kabuto that the reason the fourth could not be revived was because his soul was not in the afterlife. He stated that oroochimaru tried to revive him but failed because of this reason. The third actually did nothing to stop the resurrection.

That's pretty much it, or you could say that the coffin would've come up but it would've just been a body without a soul