Someone on the hill I live in, San Leandro unincorporated, has three limos which he parks on the streets for typically a week at a time. Since it is the hills,it is already crowded. Is there anything I can do since he is taking up a lot of space (stretch limos)?

Parking is open to anyone, first come, first serve. You could get some people together and go to a township meeting or have people sign a petition that signs be put up saying residential parking only.

Your city may be unincorporated but this website indicates that they have police and regulations and at least some pertaining to parking. Call them and find out if there are any regulations that will help solve your problem.
City of San Leandro - Community Compliance (http://www.sanleandro.org/depts/pd/services/compliance/default.asp)

I doubt that the limos are there legally because the BUSINESS is not there legally.
Put signs on the windshields that all the neighbors will have the business license taken away for operating out of a residence illegally and give him 5 days.

There may be issues, is the business licensed for this location ? If they are operating the business there, without proper permits or license, they may be forced to move the business.

Next what are the zoning laws about vehicles like this parked

Next what is the city ordinances about parking.

But in most cases, public parking is first come first serve and they have as much right to park as anyone does.

The omly way to resolve is through your city/ township.

The omly way to resolve is thru your city/ township.

OP has said that San Leandro is unincorporated. In other words, it's simply a geographical location. That doesn't seem to fit San Leandro, California (https://en.wikipedia.org/wiki/San_Leandro,_California#Government).

But in any event, yes, contact whatever local government that has zoning power.