My question involves landlord-tenant law in the State of: California

My two friends and I rented a house from our landlord and subleased the 2 extra rooms with the landlords permission to two other people from Craigslist. My 2 friends and I are the main people on the main lease with the landlord/owner of the house. We wrote a sublease agreement for a one year lease starting August 1, 2011 and ending July 31, 2012 for the 2 roommates from Craigslist.

Out of nowhere, both of the roommates that were subleasing from us decided to move out on April 4 2012. I tried verbally explaining to them that they could not just move out just because they want to and that the one year lease that was signed between them and us is a legal written contract. They brushed me off and took all their stuff and left. Now I have 2 empty rooms which they still owe rent for up to July 31, 2012. They did not pay for April's rent or utilities and they told me they will not pay for May, June, or July either.

Here are my questions:

1. We already have a couple people that want to rent the 2 rooms starting August 1, 2012, but do I have to find someone immediately to sublease for 4 months to try to make up their rent? Or can I leave it alone and sue them for those 4 months of rent in small claims court? Finding someone to live in a house for only 4 months can be difficult, do I have to at least try?

2. When will I be able to take them to small claims court? Do I have to wait until July when they don't pay all those months of rent and sue them for the full amount?

3. Can we sue them for the utilities as well? Comcast and garbage are the same amount ever month and we divided it by 5, so can we continue to add up those expenses to take to court? What about electricity and water?