Thirty years of marriage is as good a test as any of compatibility and endurance, but there should be a prize for those who throw a joint business venture into the mix. A bit like the Centenarian Bounty issued by the President on your 100th birthday, couples who manage to stay together and run a business together surely deserve some sort of extra recognition. Top of this imaginary honours list would be husband and wife team Karen Higgins and John Redmond. The former Brown Thomas alumni have worked in the same company for over 30 years but never worked directly…