Question
How much water and fertilizer do they need?I live in Ca.the bay area

Answer
Lilacs and Cestrum need slightly alkaline soil -- high pH -- and max out their genetic flower power with long term Phosphorous preferably in the form of organic matter, as in Bone Meal, when it's time to bloom.

Lilacs take years to get used to their new home.  After the first year of bloom, they become more prolific with each new season.

Cestrum -- Night blooming Jasmine -- is a fairly tender tropical plant that will take below-freezing temps for short periods of time.  It blooms in cycles.  Rests, blooms, rests, blooms, throughout the year.  Remember, it is fragrant only in the dark.

There are no special water needs for either of these.  The usual water drenching with room temperature water, followed by a dry spell to let in air molecules and keep the aerobic soil bacteria happy, is all you need to know.  Don't overwater.  You'll wipe out good bacteria, and set up a party for the root-rotting anaerobic bacteria that follow.  Drainage of course is a must.  And TONS of Sun.