Hi, First off merry Christmas

Myself and my brother love playing this game and doing hot lapping and single player races (taking turns to beat each other). But my question is i have a duel montior setup and what we would like to do is be racing on one screen and have like a live replay on the other so the other people watching can be watching a live replay while the racer is racing.

It's possible to watch a replay on one screen, and race on the other, if that's what you're asking. Just open two instances of LFS. If you want to watch the same race you're in (say a different camera angle), I don't believe it's possible unless you have two accounts. An alternative is to use LFS Remote if you're racing online.

Have a look at this post and this quick demonstration video.