Hiruzen knew this jutsu and Kushina couldnt use it because she wasn't a jinchuriki. I doubt minato made it up, he said it was a seal only a non-jinchuriki could use it seems more research was needed tha Minato would be able to do. With Chiyos jutsu research stopped because people were dying from testing it so we know that in that case it was a large team so with Minato the same if he made it but it was probably an unzumaki tech. passed to Minato before the killing of the Uchiha. Kushna could have brought scrolls of sealing from the land of whirlpools. (forgive my spelling)