From the photos they probably are Echinopsis Multiplex...but there are so many Echinopsis hybrids around that all look very similar body wise making an accurate identification difficult if not impossible ...photos of the plants in flower would certainly be a great help.
The first photo:
Further inspection of the Parent stem in the middle tells me that it is not Echinopsis multiplex, or as it is now accepted as Echinopsis oxygona nor is it the brevispina variety.
I agree with ZenOne that it's a high probability that it's a hybrid Echinopsis of which there are hundreds. Dozens of them have those same growth characteristics you have pictured.
When it blooms, if the flowers are pure all white, then the odds are higher that it will be a true species.
There are only a handful of true Echinopsis species that have color in the flowers.