@Daniel Levin could you clarify? I'm going to type away making a bunch of assumptions lol.
I am not an electrician. But I've helped do lots of paperwork and field visits with our electricians, electrical inspectors, and utilities...which means I know just enough to be dangerous! Check your plan with your local inspector, not with me.
Electrical systems are unique for each unit; usually there are many choices of how to go about separating services, especially if you are doing it sequentially instead of all at once. If you're lucky, there are already separate breakers boxes and no overlaps.
Do a search to learn about sub-metering, that may cost less and get you to direct billing a lot faster.
If you want separate services (not sub meters) - then, in many cases, going from units A&B on meter 1 and units C&D on meter 2, to (assuming you are in unit B) unit B on meter 1 and units A-C-D on meter 2 isn't any more of a hassle than doing it so unit A is by itself on meter 1 and B-C-D are on meter 2. If you can do that instead, unit A is paying directly way earlier.
Around here going from 2 units to 3 units on a given meter would likely require a new entrance cable and shutoff or breaker panel, unless that meter has a lot of unused amperage. You may find it easier in the long run to add a service now for your unit - then you'd have 3 active meters, one for A, one for B, and one for C&D. If you go in this direction, it is often easiest to prepare now for your eventual 4 meters (or 5, if you need a house meter).
Whatever you do, stay safe!