I'm so sorry about your experiences and your sort of forced move away from your country. My best friend had to do the same after being held at gunpoint at work in SA and I can only imagine your devastation.
Having been to SA and experienced the environment there myself, I would say that anywhere in the UK will feel safe to you in comparison. You don't really need to worry about that when choosing where to live - violent crime is rare here and while you will see antisocial behaviour in larger towns and cities, it is non weaponised and largely fuelled by alcohol and stupidity. I've lived in London pretty much all my life and have never felt unsafe, or been the victim of a crime. The only time I've been a victim of crime in my life was, funnily enough, while visiting my friend in SA. Go figure!
If you need to be in London for work, you will need to be in either a London suburb or in a surrounding commuter town with good rail links to London. If you both hope to earn around £60k per year then you will have plenty of options for rentals, while you get settled and find your bearings, ready to move somewhere more permanent. Those suggesting places outside of the SE are not giving you feasible options if you get London-based office jobs - we are having increasing numbers of train strikes here, and train fares are hideously expensive. If you moved somewhere like Herefordshire or Cheshire and needed to commute to London, you'd be spending nearly £1000 a month on train fares alone and hours of your day commuting. If you can't predominantly work from home in your new job, you will need to stay in and around London temporarily.
Leafy London suburbs you might like:
Richmond/Sheen/Twickenham/Kingston areas (South West London)
Ealing (SW London)
Herne Hill/Streatham/Dulwich (South London)
Blackheath/Greenwich (South East London)
Archway/Highgate/Gospel Oak/Hampstead/Golders Green/Finchley (North London)
Further out into the commuter belt, all within a 45 min train ride of London:
Hitchin
St Albans
High Wycombe
Amersham/Chesham
Bedford
Sevenoaks
Tunbridge Wells
East Grinstead
Horsham
Guildford
Farnham
Reading (surrounding villages are very nice, not so much Reading itself)
Windsor
Good luck with the move. I can see lots of people on this thread are very down on the UK, but as someone with a lot of expat friends in London who feel very fortunate to be here, I don't think we know how lucky we are. The UK is a beautiful, safe country, with amazing culture and history and stunning landscapes. We have an excellent public transport system compared to many other countries, can get to mainland Europe quickly and easily, and have access to free and good quality medical care, education and public services. Yes there is a cost of living crisis and yes there are deep social divides and infrastructure problems, but this is the case everywhere. Every country has its problems. It's important to keep things in perspective.