Very sorry for your loss.
You can't complete the sale on the property until you have Grant of Probate and I suspect that's what your sibling means re "9-12 month period for selling" but that is the case regardless of who buys the property. So selling at a lower price to the local council won't get you your inheritance any faster.
Getting Probate can take up to a year to complete, but your solicitor should be able to confirm what they expect.
Who is the executor? The sale of the property is the responsibility of the executor(s).