UYScuti, I'm 70 and remember many years ago a lot of parents were absolutely heartbroken if their children emigrated. One of my husband's cousins went to Australia where he married and stayed and his parents, particularly his mum(who was and is lovely - still alive!), was terribly upset by it. I suppose you would say they were 'upper working class', dad was a printer, and the culture then was that adult children often still lived at home with mum and dad until they married.
However they were far from hard up and were able to visit him in Aus, including going to his wedding and he also came back here for holiday and for funeral when his dad died. Mum went out there a couple of times for six weeks or so after that. She must be well in her nineties now so doubt she travels but she lives in Scotland where her other child moved and let's face it, Scotland is quite a long way away for a Londoner; she has been very happy there.
I think in previous years people felt they'd never see their child again because fares were so expensive, way beyond what people could afford. I know my mother had two sisters who went to live in Canada with their husbands and people felt like that; it was long before I was born but mum told me what a wrench it was. They wrote regularly and after I was married, the sisters' eldest daughters came over here and stayed with my mum but that the first ever visit.
One of my neighbour's children lives in Australia but they've all been there, also met him in another European country where he went for work and he's been back here. He came here with wife and baby daughter and stayed for three years (planned), had another child whilst here, it was lovely for everyone.
The world is a smaller place than it was.
The op is not (at the moment) planning to leave the UK for good, just for a while; her parents really must accept that. It will be a wonderful experience - or at least we hope so :-) - and presumably good for husband's career. It's not so much that her parents are being selfish, rather that they will miss their daughter and family so much - but it isn't forever.