Yann - if you happen to see this post, these are seedlings from your seeds. An excellent germination, I'd say indeed! :)
(https://www.e-aiand.com/kaktusefoorumisse/231113/ario073.JPG)
Here, a picture of a grafted Ariocarpus bravoanus seedling:
(https://www.e-aiand.com/kaktusefoorumisse/231113/bravoanus049.JPG)
Great work!
Keep us updated!
Dan