sweating pipe in a multi story building

Hello all, some advise here would be appreciated. I am working a remodel on
the third floor of a 17 story building. The stacks are connected to the top with no shut off per each unit. I can shut off supply to all floors by area ie: kitchen
powder room, master etc. My question is how to sweat pipe if the water drain down from the above floors will inevitably be there. Is it possible or do I need to use comp fittings? this is for shower rough ins as well as replacement shut offs for toilet and sinks. thanks Jeff

Your not going to be able to sweat with water running

What size are the pipes? Can you get your hands on a jetsweat? How much water pressure is there when the water is shut off?