Wow, that live oak looks nothing like the huge ones I grew up with in Fl. But good luck, I hope you can save them, it would be a shame to loose good material for bonsai, while building a place for bonsai! Kinda counter productive. I wish I had some help for you, but dont. I hope it goes well!
There are two types of Live Oak that grow in this region. Most common is Coastal Live Oak, Q. agrifolia, and Canyon Live Oak.
I think the main reason they're so different from the southern variety is the mountainous terrain and mixed forest they habitat. They naturally tend to grow more slender and lack the spreading crown that is common in the southern region.
It's a funny thing about the Canyon Live Oak trees is that it depends upon who you're talking to they are very different. For instance, the Audubon Society says they are perhaps the most beautiful trees in the whole Western region and truly they deserve it. However, if you discuss the trees with forest management or wild fire personnel you learn they are considered the devil's own trees. It's often referred to as 'grease wood ', and their tendency to flash into a raging balls of fire makes them extremely dangerous in wildfire situations, especially when there's entire hillsides covered with it.
From my view point they are quite magnificent as bonsai subjects and the more we remove the better.