Just follow my previous advice, make sure you stay in the roost long enough so that the Red Dragon comes back to the roost and breathes fire.
From that point run back to the stairs before the bridge and make sure your stamina is full.
Run to the other side of the bridge and don't stop because of the soldiers, once you're on the other side completely, you can defeat them, even if the dragon passes through the bridge, since he cannot touch you there.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
