Camille
These species are really to new to cultivation not a lot of people have them. You are one of the few. But, I will tell you what I know.
Impatiens hians is from West Africa and is only a seasonal bloomer, mostly in winter. In the wild it is know to grow in trees as an orchid does and also on land. Looks good in a hanging basket. I saw one at Kew in London it looked stunning as a ground cover. Flowers are large and look like funny lizards jumping out at you.
Impatiens paucidentata now this one is really rare and is an epiphyte like an orchid. Seems to bloom in early spring for me. This was the first year it really bloomed well for me. It can take some dring out, the leaves and stems are very succulent. I grow mine in an orchid mix with some potting soil it seems to like this. Its also from East Africa.
Impatiens eriosperma is from Madagascar. I have it but not really that long so I cant say much about it. I got a couple of flowers, they were red and similar to Impatiens niamniamensis but not as long.
You can do cuttings like any other Impatiens but I would highly recommend using moist perlite and covering them with plastic wrap. They should root in about a week.

Thanks a lot for these informations.
I m fond of impatiens.
I ve noticed that when I search in internet the few impatiens in selling are in england or united states...not in France excepted niamniamensis. A lot of impatiens of Annie's annual interest me but I cant buy them because I m in France.(tinctoria,...)
So, it s very difficult for me to get new impatiens excepted with nice poeple of this mailing list.... ;-)

Thanks a lot for these informations...

Good culture!

Camille.