Who will own the real estate? Will it be owned partly by you or wholly by the family member? Remember that the owner of the land is the owner of everything built on it.

If you are putting money into a property but it is not wholly or partly registered in your name, then you are either lending or giving money to the family member.
If you are receiving a pension, this may affect your pension as there are implications of lending or giving money away to family.
If you are making a loan (and not an owner) then you need to have some written agreement that confirms it is a loan (and not a gift) and what is the position if you want your money back.