So what exactly is the difference between the DUP and the UUP?
UUP is more liberal-conservative, officially secular and largely aligned with the Tories on policy. The mainstream unionist party for most of NI modern history and the governing party from 1921-1972. Much more moderate than the DUP.
DUP is much, much more socially conservative and I think more populist on economics. They were founded by evangelical Presbyterian minister Ian Paisley in the 1970's as an alternative to UUP and have kept their Christian undertones and links to Protestant churches and Ulster loyalist groups. In the last 15 years they have overtaken the UUP as the main unionist party and have moderated a bit, although they are still pretty batsh*t.