Since grandpa stuffed jade's dreamself's body through some time travel portal stuff, doesn't that mean he could have stuffed his own body through the same means?
The teleporter doesn’t work that way. He was teleproted into the future because the Medium did not exist at his time when he used the teleporter. And when he went home it teleported him right back to the time period he left. Grandpa Harley had no way to teleport into Earth’s future or even ahead of his own timeline.