It is unlikely that you have a vent problem.....plumbing vents are not designed to disburse sewer odors, but to ensure your entire waste water discharge system stays at atmospheric pressure to prevent back-ups, slow draining or retrograde flow of waste water.
The job of keeping sewer odors out of your house in a sound, unleaking system of plumbing pipes, is up to the various traps at all drain points, including sinks, tubs, toilets, showers, and other points of waster water drainage. The two most common reasons for odors to come into the house are p-traps (those sideways S-shaped pipes under your sinks) that don't have any water in them, either because the sink they are draining hasn't been used in quite a while and the water in the trap just evaporated out...or the water in the trap leaked out. Without the water in the trap, sewer odors have a direct path up into the house. Toilet traps are built into the toilet and as long as there is water in the toilet bowl it should be ok. The other reason is becuase somebody didn't put the cap back on a clean-out (usually in the basement or crawl space) after declogging a drain pipe or sometimes plumbing is added with the vent pipe run up to the attic but not out the roof....so sewer gasses get into the attic and can be smelled througout the house.
One other thing you might check for has nothing to do with plumbing....but dead animals can mimick sewer odors....such as mice. Otherwise, you should be able to localize which sink or drain the sewer odor is coming from and check that drain and p-trap to ensure it has water in it.