I would be aiming for 2 10ks in the whites spot and 2 actinics in the older fixture. For now I guess go with the 10k and 6500k ones since you have them. I would look at getting a newer fixture though, not too sure how well the nem will do. You can get a 4 bulb HO
fixture for around $100 from fish need it;lights; food;Sponge
i am using one right now over my 20g tank and love it. It would also give your nem a better shot at surviving in my opinion.
Nems will move around when they are searching for something, be it light, flow or food. if they are moving they need something they dont have in their current spot. Just keep that in mind.