Zero fast. There is no energy being transferred to the people, they would plop out and push into each other as they are forced through.
If you blocked the stationary portal then the portal moving would essentially just be a wall, no one would go though.
This whole relative thing makes no sense, energy isn’t just created because it’s observed by someone else, the door is moving not the people so them sitting there won’t suddenly be catapulted going through a moving portal, where is that energy created?