[C]ould you give me a quick answer to who the two witnesses are in Rev 11:3, and the identity of the two olive trees and two lampstands in verse 4?
I understand the Revelation to have been given c. 93 AD as an encouragement to the suffering church (under the cross, as we used to say) between the 1st and 2nd advents and I see in the book a series of cycles, which a roughly parallel (after chapter 3). I also read the symbolism in light of the original context described in chapters 1-3, where we see the visible church suffering from informal persecution from the broader culture, from Roman authorities, from non-Christian Jews, and from spiritual, doctrinal, and moral corruption from within.
I take the Revelation, after chapter 3, as a highly, intentionally symbolic book. I doubt that the Apostle John wanted us to identify these figures or images with particular people but to understand what they represent.
The two witnesses of Revelation 11 are also the lampstands (light) and olive trees (anointing by the Spirit). They recall the OT legal standard and the pattern of the suffering of the prophets and the conflict between believing testimony to Christ and its opposition. The style and rhetoric of the book is very much colored by the OT (Hebrew) pattern of parallelism, i.e., saying the same thing in different ways. Remember, the book was initially meant to be heard. Most people could not read and wide-spread literacy was more than 1500 years in the future at the time the book was given.
Thus the witnesses/lampstands/olive trees represent those who are approved by God, speaking his Word, in a sin-darkened world that opposes Christ and his spiritual kingdom.
I hope this helps a bit.