This will be the first time that we're going to try Park Hopping and make use of late Fast Passes. DCA had just opened when we were last there in 2001 and I didn't have a clue what Park-Hopping was except that our ticket allowed us to go to both parks. I didn't even know that you could go to both parks on the same day. 
So please bear with me, then tell me if I am correct or not.
Example itinerary: Pass through security and turnstile into DL as soon as the gates open. Get Fast Pass for Space Mt., but save it for later in the day. Ride Buzz, Star Tours and/or the Matterhorn first. After approx. 45 minutes, the window for another Fast Pass should come up and we can go get another Fast Pass for Indiana Jones. We could either go on Indiana through the standby line, or we can hold our Fast Pass until later in the day. We could also get a Fast Pass for Roger Rabbit because it isn't connected to the system.
DCA should now be open. I can send my 2 teens over to DCA with all our tickets to get Fast Passes for Soarin' and Grizzly Rapids (because Grizzly is not connected to the rest of the rides in DCA) They would get their hands stamped as they leave DL, and this stamp is their entrance into DCA. (do they even have to have their hands stamped?) And even though the rest of us haven't stepped a foot in DCA, they can still get Fast Passes for us because our tickets have been activated at DL...is this right?

So please bear with me, then tell me if I am correct or not.
Example itinerary: Pass through security and turnstile into DL as soon as the gates open. Get Fast Pass for Space Mt., but save it for later in the day. Ride Buzz, Star Tours and/or the Matterhorn first. After approx. 45 minutes, the window for another Fast Pass should come up and we can go get another Fast Pass for Indiana Jones. We could either go on Indiana through the standby line, or we can hold our Fast Pass until later in the day. We could also get a Fast Pass for Roger Rabbit because it isn't connected to the system.
DCA should now be open. I can send my 2 teens over to DCA with all our tickets to get Fast Passes for Soarin' and Grizzly Rapids (because Grizzly is not connected to the rest of the rides in DCA) They would get their hands stamped as they leave DL, and this stamp is their entrance into DCA. (do they even have to have their hands stamped?) And even though the rest of us haven't stepped a foot in DCA, they can still get Fast Passes for us because our tickets have been activated at DL...is this right?