If you intend to acutally install it the way you have drawn it, you are going to a LOT of extra work and expense. But it would be difficult to explain a different way and hope that you would understand and install it that way. You do NOT want to run 3" laterally and the reduce it to 1 1/2" for the sinks. And I would not run 1 1/2" to the sinks in the first place. The same thing with the 4" reducing to 2" for the tubs.