If you are paying more (or all) of the deposit, and you want to ensure that this deposit is protected for you as far as possible, you can draw up a declaration of trust which effectively ‘ring fences’ your initial deposit.  This type of declaration will stipulate that when the property is sold, the deposit should be repaid to the owner who paid it before any remaining capital is divided between the owners.   You can then choose whether the remaining capital is split between you in equal or unequal shares.
It is important to remember that if you have a mortgage, this will have to be repaid first and before your deposit.   A declaration will also not protect against the event that the property market falls significantly, leaving you with insufficient value to pay back the mortgage and the initial deposit.