You're making that correlation of them training Minato. I don't recall the manga making that statement. What I've provided was a scan of Pa having no knowledge of Minato. He wasn't even properly trained. They're obviously not beings you can simply summon, as Jman references having to "call" them.tbh if the fact minato having sm was retconned since he must have trained under ma and pa to learn it don't see why they can't be summoned by himnot to mention Minato is a kage
Believe what you want.