How can I change a single basin sink with large 60'"vanity to a double bowl sink in main upstairs bath with out having to go through walls to install second water lines to second bowl.

Hi Kimcar...

You could install new 3-way angle shutoffs (see image), or you could also install 3/8" compression tee fittings(see image) off each existing shutoff and put braided supply hoses in between to connect all up.

In terms of the waste piping, the sinks need to be no more than 30" center to center of each other to allow you to use one PTRAP and the existing vent. Over 30" center to center and you are supposed to open up the wall and install an additional PTRAP and vent. Most 5 foot vanities have sinks that fall within the 30" center to center so you should be OK.

Mark