The drawing is missing much of the venting.
You can use the vent of a lav to wet vent a tub or shower, assuming the pipe sizing is 2" or larger.
If you're not wet venting, then you would need to vent the lavs, showers, tubs, kitchen sinks, laundry trays before they enter the main stack or branch. Venting is what prevents a trap from siphoning.
The first rule of plumbing, is that for every pipe going down, there is one going up through the roof.
2nd rule is that the pipe through the roof (the vent) is plumbed between the trap (p-trap) and the common line.