First, you have to make sure the romance is installed. Open your Weidu.log in your BG2 directory with Notepad and check that de'Arnise romance is installed.
Second, check the Readme. It says
You do not need to start a new game in order to take advantage of de'Arnise
Romance if you do not wish to do so, but you will need to start the game before
the final resolution of the de'Arnise Keep plot in order to enjoy the romance
content--specifically, before you leave the keep and Nalia wonders about its
future. To be on the safe side, just so you don't forget, don't start playing
with a game which occurs after you have defeated Tor'Gal.
Did you do that?
Also, consult the readme if you're stuck in the romance - I recommend it.
Banter and Xan and Sola don't influence Nalia romance(although I'm not sure how Valen is - never played it, myself). Really, Weidu NPC mods never block each other, unless you're romancing several gals in a row in a "committed, sleeping together stage".
If you want to look up various variables, I recommend downloading any BG2 guide and learning to use the console. You could download Dan Simpson's walkthrough from sorcerers.net, BG2/walkthrough section - I recommend it. The de'Arnise variables are in the mod's readme.