In that case you should considering executing a declaration of trust prepared by a solicitor now taking account if the fact that ,although on the face of it you are the registered proprietor of the title, you each own differing percentages in the equity of the property.
You should ask the solicitor to also registered the declaration against the registered title in the form of a notice. Get them to keep a counterpart with another counterpart to be retained by you. That will put your family member's percentages outside of the matrimonial asset pool in the event of divorce. It will cost approx £150-200+VAT.
Assets acquired before marriage by an individual party become included once the marriage is a "medium" to "long" one (ie. 7-10 years as a rough guide but each case is decided on its own merits), so the longer you are married the more likely your share will be included in the settlement negotiations.
You may consider also executing a pre-nuptual agreement with your fiance to provide some additional protections, the Courts have been inclined to attach more weight to these recently.
In the end, marriage is a financial commitment which does expose your assets to risk the longer the marriage goes on, but you should reflect the respective interest in the property in the above way.
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