If the surface of your yard has a good profile that drains water away from all the buildings and is pretty level (no holes), then DO NOT TILL IT. Tilling will ruin the drainage and make holes in the future as the soil settles unevenly. How far away from the beach are you? Orange county is a big place. I have seen Kentucky bluegrass growing a few miles from the beach and it looks great all winter long. KBG would suffer more the farther inland you get. If you are east of Interstate 5 down to Irvine I would not try KBG. The eastern parts of Mission Viejo would be too warm for KBG but western parts are probably fine, even though it is east of I-5. Bermuda would grow anywhere in OC as would St Augustine. You don't have to sod your entire lawn with St Augustine if you are willing to wait. If you are not willing to wait, then St Aug sod is great for an instant lawn. As Lou said above, it is a coarse bladed grass. Bermuda and KBG are fine bladed grasses. Bermuda can be much more of a pain to make really nice simply because it looks shaggy unless you mow it several times a week. It is also very invasive and tenacious. St Aug and KBG are both less invasive and much less tenacious than bermuda. And they do not need nearly as much mowing. You are asking very basic questions so I'll give you the 1-2-3 guide to growing great turf. It is really just this easy. Water deeply and infrequently. Deeply means at least an hour in every zone, all at once. Infrequently means monthly during the cool months and no more than weekly during the hottest part of summer. If your grass looks dry before the month/week is up, water longer next time. Deep watering grows deep, drought resistant roots. Infrequent watering allows the top layer of soil to dry completely which kills off many shallow rooted weeds. Mulch mow at the highest setting on your mower. Most grasses are the most dense when mowed tall. Bermuda, centipede, and bent grasses are the most dense when mowed at the lowest setting on your mower. Dense grass shades out weeds and uses less water when tall. Dense grass feeds the deep roots you're developing in 1 above. Fertilize regularly. I fertilize 4 times per year using organic fertilizer. Which fertilizer you use is much less important than numbers 1 and 2 above.

It looks a lot like Poa Annua, but it could also be regular Kentucky Bluegrass. My KBG is flowering right now, which is consitant with your pictures (I'm in zone 7 as well) If you had Fescue sod before, it probably had Bluegrass in it(a lot of sod farmers use it as companion to tall fescue in the transition zone) and that's what you are seeing. If you sprayed roundup and killed everything, then sodded or seeded with bermuda, then it is Poa Annua. You could also have a next door neighbor ( or very nearby) with a Fescue/bluegrass lawn and contamination is very possible by seed. Anyway, if is Poa Annua, you don't have to do anything, it will die on its own with the arrival of summer and by natural causes. If is Kentucky Bluegrass however, it will persist in your climate. If you really have bluegrass and don't want it, you can wait until Fall when your bermuda goes dormant, then spray roundup on it. That will take out the Bluegrass, but will not harm the Bermuda. More information than you probably needed.

Depends on the weed and what you want to get rid of. I think you are keeping the bermuda, is that right? Besides clover, what weeds do you have?

I agree that the fescue has to go. Fescue is not compatible with California's water shortage. When fescue is grown in the right location, it only need 1 inch per week. I also agree that giving up grass for dirt is a foolish idea. Brown dirt heats up the air eventually leading to more use of air conditioning and likely water inside the house. Another problem with California's rules, as I read them a while back, is that they do not allow you to water properly. Our toughest water restrictions in San Antonio allow us to water every other week for a total of 6 hours per day. Our most lax restrictions allow us to water every week for a total of 8 hours per day. This regimen absolutely works for most grass unless it is mowed too short on a south facing lawn in full sun. From my understanding of the California rules, you can only water for 10 minutes. That is EXACTLY wrong. Even in Phoenix the deep watering rules work. In fact I'll tell you a method that works great - soaker hoses. Turn on your faucet to the water trickles out at 1 cup per minute (roughly 800 gallons per week), run a hose to a soaker hose and let it run for days at a time. Keep the soaker hose moving and you'll have a pretty nice lawn for only 800 gallons per week. Otherwise the normal practice that works is deep and infrequent watering. Deep means a full inch all at one time, not 10 minutes per day. Infrequent means once per week with temps in the 90s, once every other week with temps in the 80s, once every 3 weeks with temps in the 70s, and once a month at temps below 70. As to a grass for your situation, if you remove every tree pictured in your pictures, then you can have bermuda. Clover is not going to be particularly happy with 1/2 day of sunlight either. There are two grasses that will be very happy in your situation. Those are St Augustine and a variety of zoysia called Shadow Turf. St Augustine is inexpensive, easy to establish, and grows with a coarse blade. Shadow Turf is expensive, easy to establish (but takes much longer than you expect), and grows with a fine blade like your fescue. Shadow Turf will not take much wear if you have pets or walk the same path every day. It will shorten as the grass blades break off and it will not return until the following spring. St Augustine will show a path but will return within the same season if the activity stops. Just out of curiosity where are you in Riverside. I grew up between Central and Arlington west of Victoria. My sister lives down towards the airport.