I think you can only avoid a house when you go into care if you were living there and you had no where else to go. A lot easier if there is a spouse.
It will be worth talking to a solicitor to put the house in trust to avoid this. Wish we had done that for my mum's place. However, if there are signs that your mum's health is getting worse you may not be able to avoid the house being used to fund care. Acting as early as possible is the best advice you can have. Care has cost my mum in excess of £150K so far!
The other alternative might be for you to buy the house outright for your Mum. Thus allowing your Mum to have some extra income to enjoy or distribute to you and your brother. If you have a property and an older relative lives in it and you pay for everything I believe you can avoid paying capital gains tax. Your Mum will not need to pay for care if she has spent all the cash before she gets to that stage.