A few points:
1. The actual physical deeds to a house are now largely irrelevant; it's the Land Registry's records that are all-important.
2. Adding the names of yourself and your brother to the title document is a fairly straightforward process, which involves little more than filling in a form. Even so, your mother would need the services of a solicitor to ensure that everything was in order, so some cost would be involved (but not a particularly big one).
3. Properties can be owned by more than one person either as 'tenants in common' or as a 'joint tenants':
https://www.gov.uk/joint-property-ownership/overview
From what you've written, your mother needs to ensure that the title document is amended to show you all as joint tenants (and not as tenants in common).
However that means that when she dies first (assuming, of course, that she does) you and your brother will then be the surviving joint tenants. When one of you then dies, the whole of the property will pass automatically to the survivor. (i.e. neither you nor your brother will be able to leave your 'share' of the property to anyone, since you won't own any such share. It will be your legal 'partnership' that owns the property, with the surviving partner automatically owning the whole of the property upon the death of the other).
4. If your mother dies within 7 years of effectively gifting part of the house to you and your brother, the value of the gift (decreasing on a sliding scale as time goes by) will still count as part of her estate when calculating any liability for inheritance tax. However if the total value of the estate comes to less than £325,000 there won't be any inheritance tax to pay anyway. (If the whole of your father's estate passed to your mother on his death, she also gets his inheritance tax relief, so her estate could total up to £650,000 without any inheritance tax needing to be paid).
5. Even with the house transferred into joint ownership (as joint tenants), I'd still strongly advise that your mother should write a will.