All the zoning tells you is that your property is in an area where four units are permitted on one land parcel.

You will only know for sure whether a conversion of your existing dwelling or creation of a new four-unit dwelling is possible when you submit an application for a permit. If you contact the planning office, a planning tech will give you a decent idea of whether such a permit would be issued.

Some people think that if they have a property in a zone that allows for x number of units, they can simply just do it. That's not the case. You want to end up with a legal four-unit dwelling, and you can only get there via the permit process, and you have to comply with building code when you do the conversion or they won't issue an occupancy permit.