My fiance's dad was born in Cambridge (UK) while his dad was in the US airforce and his mom was a local (UK born). Would he qualify for a visa based on his dad's place of birth and grandmothers? His father's birth certificate states that he was born in Cambridge instead of an air force base. And my fiance's grandmother lived in Wimbledon until she moved to the US. I'm not sure what the rules would be for visa requirements are in his case.
The status of his parents isn’t quite clear. If his mother was “a local born in the UK” and it means she is a British citizen, then the son inherits British citizenship from her. He is British. If he was himself born in the UK, then he is British citizen “not by descent” and his children inherit British citizenship from him. If he is born outside the UK then he is only “British citizen by descent” and his children only have British citizenship if they are born in the UK.
Since his father isn’t British, it doesn’t matter where he was born as far as UK citizenship is concerned.
Sorry, got confused. All the above actually applies not to the fiancé but the fiancé’d dad. It seems your fiancé’s dad was British not by descent, which makes the fiancé British by descent. He is British citizen. He can just get a British passport. And about the only people in the world who can’t get a UK visa are British citizens - because they don’t need one.