It will help if you post a photograph.

I agree with Christopher. Established residential properties often have an "eclectic mix of old trees". In fact, "eclectic mixes" or a collection of various species is typically the norm rather than the exception! I seldom suggest removal unless the trees are unhealthy/in decline or blatantly improperly sited.

Often it is helpful to treat them as the specimen plant (or singular, unique feature) in a particular location and then anchor them with other, smaller plantings that will tie them together. Could be as simple as a groundcover or as mentioned above, the repetition of other, smaller plants throughout the garden. In a smaller LA garden, removal of any turf and replacement with hardscaped walkways and a groundcover might be all that's required. The trees will look unified and the garden will be calm, uncluttered and low maintenance.

Or if you have greater space than I imagine, it is possibe to create a series of individual garden 'rooms', each featuring a particular tree, and turn each 'room' into its own character. Much more design effort involved, a bigger plant palette needed and increased maintenance required.

thank you all this is very helpful.I will go with the unifying ground cover/hardscape (large rocks) and tie in some repeated smaller plants to make it work. I really did not want to uproot these big beautiful trees but i am craving unity., happy there is a way to have both Thanks for the suggestions.

Meandering peagravel pathways through the areas you create and possibly a bench or large boulder for seating along the way will also give it a peaceful aura. Plant some native species which attract butterflies.

Steak, If later you want specific advice, start a new thread for the area you want to work on. Include pictures that span the entire scene. So as not to have the camera too away, usually it's best to take a series of slightly overlapping pictures that show from end to end, where the camera would stay at the same central (for the scene) location, merely panning.