When selling a California registered vehicle, the registered owner of record must:
Release ownership by signing on line one of the title.
If the vehicle is, or was financed, a name will be in the legal owner section and their releasing signature is required on line two.
Provide the purchaser with evidence of a valid smog certification.
Smog certificates are good for 90 days from the date of inspection. The smog certification is not required if the owner or buyer signs a statement that smog certification was submitted with renewal fees within 90 days prior to the transfer date (a vehicle inspection report may be required for proof of certification).
Provide the odometer mileage if the vehicle is less than 10 years old (Vehicle/Vessel Transfer and Reassignment Form, REG 262). If the title does not have a designated space for this information, a REG 262 reporting the odometer mileage must be signed by both the seller and buyer. The REG 262 cannot be copied. An original must be submitted. To obtain a form by mail, call DMV's automated phone service 24 hours a day, 7 days a week at 1-800-777-0133. To speak to an operator call between the hours of 8 a.m. and 5 p.m. Monday - Friday, Pacific Standard Time, or pick one up from your local DMV. If calling from outside the United States, please call 916-229-0370.
Complete a Notice of Release of Liability (REG 138) and mail the notice to the DMV address on the form. The seller is responsible for reporting the change of ownership to DMV within 5 days from the date of sale. It is important to do this as soon as possible, because after DMV updates the information from the REG 138, you will be cleared from future liability on the vehicle. The purchaser is responsible for reporting the change of ownership to DMV within 10 days from the date of purchase.
I doubt there's any problem with giving them the VIN number. They can get it off your car anyways if they come to see it.