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You as a family can deal with the necessary paperwork, although you may need to use a SOlicitor to deal with the appropriate Land Registry form and application if you ar enot familiar with it yourselves.
Firstly, whoever is appointed as Executor(s) in your Mum's Will, will need to apply for Probate. This can be done by making an appointment at your local Probate Registry.
Once Probate has been obtained, and on the basis that the 3 of you do agree that the property passes to you, in return for their one third share, the Execuotr(s) will need to sign a Land Registry Assent form- officially called an AS1. This is the document transferring the ownership of the property to you and should be dated on the day you pay your brothers.
The AS1 will then need to be sent to the Land Registry with the application form (called an AP1) and fee, and the Probate document will also need to be sent.
You may wish a Solicitor to prepare the AS1 and submit the application to the Land Registry- he would likely charge approx £250-£300 plus VAT.
I hope this assists you and answers your question.