I doubt very much if you would be able to arrange a transfer to your brother. Halifax are accommodating when it comes to divorce and transfer of equity between partners and new partners but quite frankly what you are dealing with here is the fact that your brother is happy to buy the property from you and your wife so you can move to a bigger property and thats how the lender will see it too.
He will need to be credit assessed and affordability assesed and then underwritten and he will hav to choose a new mortgage product to use. He cannot just continue wth the previous product tht you had. This will also be subject to any deposit he has or if you are gifting the equity within the house to him.
If there is no equity in the house then the chances are that Halifax or any other lender will not take the risk on in the first place. If you bought at 90% 5 years ago it is very likely that the property is now only worth about £75k, maybe even less and so in order for him to take on this mortgage he would need to be assessed to take on the mortgage of £75,000 minus a minimum deposit of 10% meaninbg a mortgage of £67,500.
This unforunately means that you would still owe the lender money (difference between sale price and mortgage balance)after the sale which would need to be repaid before you would look at the purchase of a new property or if not repaid would be assessed a a financial commitment when assessing your affordability for any new house purchse.