1. your demo should be to get to choke and land a sticky on flank as the scouts are trying to get through and well before the soldiers ever arrive. this shouldn't be terribly hard to practice since since the jumps aren't very technical like on badlands/obscure. if he still gets bombed by the soldiers because he didn't do enough damage with his initial stickies (very likely), it's not a bad idea for him to just back out through choke and have your soldiers counter bomb their soldiers.
2. jump when they're not paying attention. if the other team is already staring at your soldiers, they've already done their job.
3. you can try having your medic rotate immediately to choke through the elbow thingy to meet up with your demoman and maybe scouts at choke. that, or rush up immediately through the wooden planks to their choke. whatever you do, don't sit for an extended period of time on the lower ground.
4. height advantage is key to winning this map.
5. if the other demoman is shitting on your combo too hard, it might be a good idea. it's much easier to do damage in general from choke though.