Given that your aunt appera to have had the right to stay in the property for life, I would say that you have an interest in possession trust created during your aunt's lifetime. Normally, that would mean that on her death, the value of the property should be included in her estate for Inheritance Tax purposes with that value also forming the cost for CGT purposes for you and your brother.
IIP trusts created before 22 March 2006 were potentially exempt transfers which means that the value falls out of the donor's estate after seven years. However, your aunt was a beneficiary with a life interest as well as being the settlor so I cannot see how the gift into trust would not remain as part of her death estate, one way or another. In effect, she was giving nothing away.
I don't believe that the trust will have a CGT liability unless it sells the property as opposed to you and your brother selling it. It might have to do that if there isn't enough cash to pay the IHT liability if there is one, then iAs far as I can see, the property is now owned by you and your sibling.
Take a look here, here, here and here for information on interest in possession trusts
I hope this helps but let me know if you have any further questions.