There are actually 3 companies, Angel City Flyers (I'm doing the internship there), UKFT (I believe there is also a company based in Florida with the same name but no relation) and PCH (Japanese only flight intruction).
All four companies share the building but to the best of my knowledge UKFT doesn't have a specific office or space within the building.
Rainbow as two sides to it, the flight school and the air ambulance/charter side. The majority of the people at Rainbow are on an internship program. Usually the deal is 1,000 hours of instructing after getting their CFI/CFII/MEI and then onto another company to get line training and 250/500 hours turbine time.
The fleet includes 4 C152's, 2 C172's, 3 C172 SP's, 1 Warrior, 2 Archers, a Seneca and if I've missed anything out I apologise. The interns at Rainbow get the chance to fly a King Air 90 or 200 after they are Multi-Instrument rated.
There were 3 Robinson R22's until recently, one went back to the leasing company leaving two. I'm unsure if there are any plans to get hold of additional helicopters or different makes/models. I personally have never seen anyone at Rainbow be given Jet Ranger instruction from a Rainbow instuctor.
The director who runs the flight school side of Rainbow has, so I've been told, is the world's most experienced R22 pilot in terms of hours logged. There are two other helicopter instructors
ACF, PCH and UKFT rent aircraft from Rainbow, keeping costs down, and allowing them to use other schools at the airport (California Flight Centre, Long Beach Flying Club, etc) if a Rainbow aircraft is down for maintainence. I am unaware if the other two schools have done this when required, however I went elsewhere for my Multi-Engine checkride when the Rainbow Seneca was down.
ACF have recently acquired a Cessna 172 with a glass cockpit Garmin 1000. Due for delivery mid-August.
UKFT also contracts rainbow instructors, ACF and PCH do all training inhouse, however have a reciprocal agreemet with a Japanese Rainbow instuctor if she is required to cover busy periods with PCH.
In terms of simulators ACF owns a G501 simulator and another based at Torrance airport, has a Garmin 1000 simulator on order from Elite (due to be operational in September). There are no helicopter sims on the site.
A few of the helicopter interns have ben promised turbine time when their instructing is finished, another few guys looked into a scheme with a guy based in El Monte who is a ferry pilot for Robinson delivering R44's. He puts qualified pilots under the hood and charges them $200 approx per hour, a third of the price of R44 time in the UK I'm led to believe.