After you have shut the water off...turn on the highest sink in the house...then turn on the lowest one.

All of the water should clear at that time or a short time later...

You can get a shark-bite with a shutoff valve that can be installed ahead of the pipe you need to repair...

Then try to solder again...

Shark-bite fittings work well...

A lot of plumbers do not like them and it is mainly for cost reasons and the fact that with them you really don't need to call a plumber...