Me thinks: stop with the caboose before the junction. Un-couple the caboose. Restart the session as the caboose takes off down the hill. Take a lesson, to heart, to save frequently.
Stop with the caboose before the junction, set the brakes. Watch everything go sliding back down the hill.
Activate the sanders as the rear (pusher) locomotives approach the siding stop. I think they are needed later.
(Chorus) Sanders, roll to a stop. Set brakes. Wait a few minutes. If nothing starts moving on its own (yeaaa) uncouple the caboose. Everything still stopped? Cool! Hit the throttle (about 3 or 5), release the brakes and pull away. Is the caboose stationary, is the train going forward? Sweeet. Move the train past the switch, but not very far. If you go too far, it will end the game.
Switch the switch. Wonder where the caboose went. Curse! Game ends, something about speeding. Found the caboose.
Chorus... Caboose stayed. Start backing the helper engines down the siding. Stop close to end block. Disconnect. Note "X"s on the two helper engines. Swear!
Chorus... go past the junction, with the intention of using the pusher engine parking the caboose on the main line and than moving the helper enginesin to the siding. No go. It either takes off, or end games.
End game. Decide to go for a beer, realize that I don't drink and my car is in the shop.
Magnum PI is on....
For a straight answer, I believe, you need to drop the caboose on the main line, drop the helper engines in to the siding, get the caboose, and continue the trip.
I did all the above on Trainz19. I don't like that when I restart Trainz A New ERA, that it will only restart in DCC Mode.
I hope that helps.
-JJ