I feel like you are spelling this out for us, but I am too thick-skulled to make it work. Hopefully somebody is smarter than me and can put it together; I will summarize what I think we’re looking for:
1. A 6 letter ME character name of a minor character mentioned in Unfinished Tales with a couple of backstories thrown out at different times by JRRT. That person’s name can also be added to another word to form a location (such as Dol Guldur).
2. Take the name from #1 above, and swap 2 letters (as in ‘water -> tawer’ in your example).
3. Change 1 letter from #2 above (as in ‘tawer -> tower’ in your example).
4. Step #3 has now provided us with another ME character name that can also be added to a word to create a place name. It must also be 6 letters long as we haven’t added or deleted any letters, and as an added bonus hint, was adapted by Turbine for a NPC name.
5. Steps 1 & 4 have provided us with 2 unique, 6 letter long character names that make up the 2 word clue, which we can then proceed to solve.
Amroth seems like a prime candidate to me for Item #1, but after flubbing around I wasn’t able to make much sense out of any letter-swapping exercises, so I may be barking up the wrong tree here.