Drain Pipe Question

So I have 3 inch main DWV pipe leaving my house to the city sewer under my slab. I want to add more toilets to my house, I'm total I want to have 4 water closets, 7 sinks, 2 Dishwashers, a laundry, 3 showers, and a basement floor drain. I think I need a 4 inch pipe to do so. If that is true I assume I cannot run a 4 inch pipe to he foundation footing and connect to the 3 inch pipe to the sewer. If I understand you cannot downsize the pipe downstream.

Is there anyway to do this without digging up the pipe from my house to the street? Trying to plan a basement apartment.