Thanks for your reply.
From a legal point of view, there is of course nothing stopping your Mother gifting you the required monies to help finance the property (although your Mortgage Lender will insist on receiving a letter signed by your Mother confirming that this payment is a gift, and is not repayable). This may upset your Brother.
Subject to the above, as you will be having a Mortgage, it won't be possible for you to grant your Brother any private Mortgage over the property (ie any private Mortgage could say that as and when the house is sold, your Brother should receive £x). This is because your Mortgage Lender won't agree to allow any third parties to have a financial interest in the house.
You would therefore have to draw up a separate Declaration of Trust between yourselves and your Brother, stipulating that as and when the property is sold, he should receive £x or stipulating a different agreement, depending on what you all can agree on.
Other than this, I am not sure how much savings your Mother has, but she can of course make a new Will, stipulating that your Brother should receive the first £70,000 on her death, but I am not sure if she has this amount of money to leave.
I hope this assists and sets out the legal position.
Family matters are always the most tricky!
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