How much stamp duty do I need to pay if I own part of another property?

First-time buyers’ stamp duty relief is is available on properties costing £500,000 or less and charges 0% on the first £300,000 but 5% on the amount between £300,000 and £500,000. Photograph: Yui Mok/PA

Q I am currently renting with my civil partner and we are looking to buy our first property together. Along with my sister and parents, I currently own a 7% share (equivalent to £17,000) in a flat that was bought in cash with inheritance that my father received after the death of my grandmother. Although my parents gave me the money equivalent to my share of the property a few years ago, I’m still on the deeds to the property and am in the process of removing myself from these.

What I’m really hoping you can help me with is working out how much stamp duty my partner and I should expect to pay when we buy our first property. Does my name being on the deeds to the flat mean we aren’t eligible for first-time buyers’ relief? Does my having owned a share of the property mean that the new property will count as a second home?