Assuming that the legal problems are cleared up then there are still a couple of things to also point out.
I love Hove: Is there a way of leveraging this to fund a deposit to buy as a first time buyer?
You are not technically a first time buyer any more as you have your name on the title deeds of this property. While there will be some lenders that will honour you as a first time buyer and offer you first time buyer products the unfortunate thing is that your dad has unknowingly cost you £2,500 in tax liability.
As your name is on the Land Registry for your dads house it means that you will not have any exemption to Stamp Duty Land Tax (SDLT) as you lose your exemption once your name appears on the land registry. This will also remain true even if your partner has never owned a house previously and as such it means that on the purchase of the property at £250,000 you will be liable to 1% Stamp Duty Tax = £2500
I love Hove: I had heard that I can leverage this percentage, without having to pay it back as it would come to me in the future anyway.
Assuming you were looking to borrow this money through a secured loan lender or bank. The lender is going to want the money back in repayments every single month. You will not be able to defer this. I di understand the legacy may be yours but if you borrow the value through a 3rd party (lender) then the lender is going to put a legal charge against the whole property until they get their full loan paid back
You will also need to note that if you do borrow the value of the deposit for the new house of say 10% of the purchase price (£25,000) and if this loan is costing you £250 per month at a rate of 10% over 15 years then this is going to affect your affordability quite a bit. Assuming you earn £27,500 each your combined net income is approx £1750 per month (£3500 joint) If you then pay £250 per month out of this for a loan then this knocks your joint income down to £3250 which is then the equivilant of an income of about £24,000 (£48,000 joint) and this would now mean that your affordability would probably only stretch to around £190,000. This figure would also be subjuct to reduction if you have any other out standing commitments such as loans and credit cards and also if you have any dependants.
Think very carefully before you commit yourself to anything.