Sorry for your loss...
Please be aware that the Revocable Trusts becomes irrevocable after your parents died.
There is no inheritance tax neither on the federal level nor in California. Inheritance is not taxable income and should not be reported on your tax return.
Assuming your parents weer living in California - California doesn't have estate taxes. Federal estate taxes are for estates with total value above $2,000,000 (for decedents died in 2008)
Only if the estate includes any tax deferred accounts - such as IRAs, 401k, etc - and beneficiaries would take any distributions from these accounts - the distributed amounts would be taxable income.
As the Personal Representative you may want to become familiar with the IRS publication 559 - http://www.irs.gov/pub/irs-pdf/p559.pdf
Please let me know if you need any clarification.