Hello and thanks for using Just Answer.
My name is ***** ***** am happy to assist you with your enquiry.
If the 3 of you agree, there is no reason why your other sibling can't inherit the whole Estate.
You all would need to sign a Deed of Variation (which can be done anytime within 2 years of your Dad's death), varying the terms of the Intestacy and confirming that your 1 sibling is to receive the whole Estate.
A local Probate Solicitor is likely to charge you £250-£350 plus VAT to prepare the Deed for you.
I hope this assists and sets out the legal position to you.
Can I assist you any further?Kind RegardsAl