My boyfriend has mentioned he is planning on getting a joint mortgage with his sister when his sister wants to buy a house (in London). They’re in their late 20s/early 30s. His sister is currently single and lives at home with their mum and covers the bills while mum covers the rent. She paid off all his student loans and that’s why he feels indebted to her and he’s been trying to pay her back these few years. He mentioned his sister’s income alone would probably not be enough for her mortgage and that’s why he might get the joint mortgage. However he also wanted us to get married in the next 2-3 years. I’m not from the UK and only lived there for a year when I did my masters. I’m still in school now in my home country (early-mid 20s). His job requires him to move across the country and he has not reached a stage where he can have a stable location yet. We’re both in a career that has lots of licensing requirements, and I might move to the UK or he might move to my country or we might both head somewhere else – all unknown and it’s very competitive. If I head to the UK I would be on a lower pay/unstable job contracts as I’m internationally trained, but if he manages to move to my country then we will both make higher incomes although my city is very expensive. I was wondering whether anyone else has done this and what would this imply for me – if we were to get our own mortgage in the UK or somewhere overseas? Also my home country is conventionally regarded as some sort of tax haven, what will be the tax implications?