Fortunately, you only need two
Sometimes, a two-dwelling-unit property will require three meters, as NEC 210.25(B) prohibits having loads that are common to both (all) tenants (such as an apartment building's fire alarm system, a shared laundry area, or exit lighting in a corridor or shared stair) run from a tenant's electrical service equipment, and many places prohibit this as well as a function of landlord-tenant law. Fortunately, in your situation where you have two detached dwelling units on the same property, the only plausible shared load would be freestanding (i.e. not attached to one house or the other) outdoor lighting, and since you don't have any of that, a two-meter pack will work for your application.
As far as specific hardware goes, the most cost-effective thing I've been able to find for this job is the Siemens WEP4212 -- at the time of this posting, you should be able to get one for somewhere around $1000 through your local electrical supply house (perhaps less, perhaps somewhat more).
Mounting this thing
Unfortunately, you'll have to work with PG&E to rearrange your electrical service into what's called an "underground service dip". This is because PG&E document 025055 prohibits service equipment larger than 225A, or any multi-meter equipment, from being pole-mounted; instead, you'll have to "dip" the service underground to an adjacent location where a suitable mounting arrangement (backerboard or horizontal struts, with pipe or timber supports) can be installed.
The aboveground (mast) section of conduit on the existing pole will need to be 2½"; galvanized rigid metal conduit with a mating weatherhead, as PG&E does not accept PVC or EMT for service mast duty; it is permissible to run Schedule 40 PVC once past the sweep from the pole into the trench though. Once this is done, PG&E will run its conductors from the existing service point, through the conduit, to the pull section in the new service equipment.
Getting grounded
You'll also need to run a grounding electrode system at the meter rack. This consists of two 8' ground rods driven 6-8' apart and connected to each other and to the meter-pack hardware by a 2AWG grounding wire. You may need to use a length of ¾"; rigid steel conduit with Bridgeport MCH-075 grounding hubs at each end as a damage shield for the aboveground section of the grounding wire, as well. If not, you can use a Bridgeport MC-075 to bring the grounding conductor into the box; either way, you'll want to punch or otherwise cut a ¾" trade size knockout (1⅛" actual hole size) in the bottom of the meter-main, below the center compartment that contains the grounding wire lugs, as service grounding fittings and concentric knockouts don't mix very well.
Homeward bound
The wiring from this meter-pack to the homes in question will be a 4-wire feeder -- fortunately, mobile home feeder cable is a readily available and inexpensive solution to this problem, as NEC 310.12 applies to individual dwelling unit feeders in a multifamily property. Protecting this wire will require a 200A QS and a 100A QP breaker of the appropriate interrupting rating for your location, something you'll have to ask PG&E about since they don't publish any guarantees on that for non-single-family properties.
Once you reach each individual unit, you'll then be able to land the wire into a main breaker subpanel of the appropriate rating and size -- I'd recommend a 30 space, 125A panel as a replacement panel for the existing home if the main panel there cannot be converted to a subpanel by pulling the bonding screw and moving the existing grounding wires to a new, separate grounding bar, while the new home will get a 40 or 42 space, 200 or 225A panel fitted.
