Joint owned property Gains- Father (main residence) Son (second residence)

Hi, In 2017 my father, mother and myself entered into an agreement to jointly purchase a property for them (215k with equal shares. At the time it was a second property for them and for myself so additional stamp duty was paid and we became joint tenants. In 2024 my mother died passing her share of the property, now fathers main residence, to myself and my father. I'm contemplating buying my father out of the property so he can live their rent free for the duration of his life, the property is now worth £300k (though we spent around £45k making the house liveable - new electrics, gas, plumbing etc). My dad is quite happy for me to buy him out of his share for £107.5k, half of the original purchasing price. Will I pay SDT again on this 107.5k amount even though we paid it the first time as a second home and secondly if i sell the home in 3 years time and its worth £350k say what capital gains do i pay - Or is it best just to inherit my fathers share on his demise and if so do i still have to pay CGT on my now inherited share from my dad?

Hi,
You would need to consider the guidance at CG14530 - Consideration for disposal: market value rule onwards, when working out if your father has a gain after private residence relief is applied.  (HS283 Private Residence Relief (2024)).  
There is a calculator at Tax when you sell property to help you work this out.  
As this is a second property for you, you may have a capital gains liability, if you dispose of the property.  
We are unable to advise on stamp duty in this forum.
Thank you.