Hi Tracey - I am sorry to read of your loss. I'm assuming that your Mother is still alive and if so then the legal ownership has passed to your Mother to deal with and probate is not required to deal with the property.
The legal ownership is always dealt with as a whole. It is the beneficial ownership that can be split in the way you described.
If the property is to be transferred then it would require a Transfer (form TR1) by your Mother to herself plus you and your brother. Our
online guidance explains what's required
The reason I say 'If the property is to be transferred' is that it is always recommended that you all seek legal/financial advice before deciding on what to do. We deal with the outcome of such advice and once you have decided what's best.