Phoenix Down Syndrome

[ReloadPsi]

Tifa: "Cloud, quick, Phoenix Down!"
Cloud: "No."
Tifa: "Why not?"
Cloud: "Because I'm not."
Tifa: "Why not?"
Cloud: "Because I'm not."
Tifa: "I know you are, but why not?"
Cloud: "Because I'm playing the guitar."

I think its sensible that Phoenix Down would only revive one from KO rather than from death

However I dont understand why they didnt try a SOFT on RedXIII's dad

Because he had poisoned arrows stuck in him that turned him to stone. Applying a Soft would've probably caused the arrows to take effect again immediately, and pulling them out would've been impossible as pulling an arrowhead out of a stone statue would require you to chip a lot of it away, especially given how arrowheads are usually designed so that they can't be removed without causing even more serious harm... this would then cause the cumulative injuries caused by such an endeavour to kill Seto as soon as they threw another Soft.