I would like to get more latitude from my badly exposed negatives by combining a few copies taken with different duration and combine them into NLP to get an HDR base to get crushed blacks or regain details in the whites. It may be unnecessary, I am still new to the transfer process, but my only way is to do the HDR in Lightroom, which creates a DNG file that is not seen well (or at all) in NLP. Still working on this for solutions.
Welcome to the forum @Daniel_Quebec
I’ve tested combining multiple exposures with underexposed negatives and found that results can occasionally produce more saturated colours in the converted image. There’s also a possibility of slightly different hues, but in most cases, I needed post-conversion adjustments to make images look to my taste.
My lesson learned is that multi-exposure HDR is not worth the effort in most cases … and your mileage might vary. Go ahead and try, read posts about effects of ETTR, there is a wealth on information in this forum.
Imo, NLP is a great time saver and occasionally needs fair amounts of post-processing.
I’ve done this often, successfully, and it’s not difficult (otherwise I would not have succeeded!) 
The keys are two things: (a) whether you really need it, and (b) the sequence of steps needed to implement it.
It’s trickier than one may think to know whether this is necessary. It’s only necessary if tones are climbing either side walls of the histogram. But the histogram displays we see are usually designed as shrunken gamut displays (say akin to sRGB), while our camera sensors accommodate much more dynamic range than these histograms contain. So the solution to this problem is to view the raw file in a true raw image decoder such as RawDigger (https://www.rawdigger.com/) which shows the full dynamic range of the raw file. If Raw Digger shows clipping, then an HDR exposure makes sense. Or, it may come close to clipping, in which case it may still make sense in order to reduce the stress on post-capture adjusting.
So, let’s say you notice some clipping or near clipping in the histogram inside your tethering application or your camera from which you will be making the exposures, and you want to do an HDR. It requires only 2 captures: (1) a capture with an exposure that eliminates clipping at one end of the histogram and (2) another capture with an exposure that eliminates clipping at the other end of the histogram. Open these two captures into Lightroom (LR) and white balance them in the usual way. Then select the two of them and open the PhotoMerge>HDR Merge tool in Lightroom; leave all options switched off and just click MERGE. The result will be a merged DNG file in LR. Open the DNG in NLP and CONVERT it. Make any further adjustments needed using the EDIT panel in NLP first. It may be all you need. If not, you can further adjust in LR or PS in the usual ways.
Thank you. It clears my issue. For the quality of my negatives, I am investing too much time and I realize, by reading you and Mark (next post), that I want too much. I’ll focus on the white balance, it will be enough. My issue : I am partially colour blind, which makes it hard on subtleties! But it’s my own trouble
Thank you Mark. You help me understand better what to do and what not to do. As I wrote in the other reply, I want too much, and both of you are just telling me that it is not necessarily worth it, especially for the value of my negatives. Thanks for the tips!
You are welcome, and hope it goes better for you.